Light-emitting device with transparent substrate

ABSTRACT

A light-emitting device includes a transparent substrate having a first surface and a second surface opposite to the first surface. A light-emitting element is provided on the first surface of the transparent substrate and emits light. A porous layer is provided on the second surface of the transparent substrate, the porous layer including an organic material and having pores. The porous layer does not include an inorganic compound.

This application is a continuation of U.S. application Ser. No.14/574,476, filed Dec. 18, 2014 and claims priority to Japanese PatentApplication Nos. 2014-004451 and 2014-004452, filed on Jan. 14, 2014,the contents of which are hereby incorporated by reference.

BACKGROUND

1. Technical Field

The present disclosure relates to a laminated substrate, alight-emitting device, and a method for producing a light-emittingdevice.

2. Description of the Related Art

In general, display devices, such as liquid crystal displays (LCDs) andorganic electroluminescence (EL) displays, have structures in whichvarious layers, such as an electrode layer formed of a metal thin film,a thin film transistor (TFT) layer, an insulating layer, alight-emitting layer, a sealing layer configured to prevent thepenetration of water or oxygen from the outside, a color filter, apolarizer, and a protective layer configured to prevent damage due tomechanical stress from the outside, are stacked on a substrate, forexample, a glass substrate or a plastic substrate (for example, seeJapanese Patent No. 4870156).

The formation of electronic device elements on plastic films (plasticsubstrates) results in electronic devices characterized by, for example,being lightweight, thin, rugged, and flexible. Such electronic devicesare collectively referred to as flexible electronic devices. In recentyears, the development of flexible electronic devices has been activelypromoted. Examples of electronic devices include displays, photosensors,and radio-frequency identification tags (RFID tags).

Methods for producing such electronic devices including plasticsubstrates are broadly classified into three methods. A first methodincludes temporarily fixing a plastic film on a supporting glasssubstrate, forming an electronic device element, and then separating thesupporting substrate. A second method includes forming an electronicdevice element on a plastic film without using a supporting substrate. Athird method includes forming an electronic device element on asupporting substrate and then transferring the electronic device elementto a plastic film.

In the second method, the electronic device element is directly formedon the film by, for example, a roll-to-roll process. The dimensions ofthe film are easily changed because of the absence of a supportingsubstrate. Thus, the second method has problems with the accuracy ofdimensions in pattern processing and the accuracy of registration ofpatterns. In the third method, when the electronic device element formedon the supporting glass substrate is transferred to the plastic film,the plastic substrate that supports the electronic device element istemporarily not present under the electronic device element. Thus, theelectronic device element is likely to break at the time of transferbecause of its low mechanical strength. This occurs markedly at a wiringportion that should be arranged outside the plastic film in order toestablish electrical connection. In the first method, a conventionalapparatus for producing an electronic device can be used, thussuppressing investment in equipment. Moreover, the electronic deviceelement is fixed on the supporting glass substrate in the productionprocess, thus resulting in excellent dimensional stability duringprocessing. After the separation of the supporting substrate composed ofglass, the mechanical strength is maintained because of the presence ofthe plastic film. The first method has the advantage that the device canbe easily produced.

In the case where an electronic device is produced by the first method,it is necessary to separate a supporting glass substrate after theformation of an electronic device element. In this case, however, ahigh-temperature heating step and so forth are performed in the processof forming the electronic device element after the temporary fixation ofthe plastic film on the supporting glass substrate. The plastic film andthe supporting glass substrate are less likely to be easily separatedfrom each other because of high adhesion between the plastic film andthe supporting glass substrate.

To address this problem, Japanese Patent No. 4870156 discloses a methodfor separating a supporting glass substrate by cutting a contact portionof an interface between the supporting glass substrate and a plasticfilm with a laser.

To more stably performing the separation in the method for separating asupporting glass substrate with a laser disclosed in Japanese Patent No.4870156, Japanese Patent No. 3809681 discloses a separation-promotingmethod in which an amorphous silicon layer is provided between asupporting glass substrate and a plastic substrate, and laserirradiation is performed to generate hydrogen gas from the amorphoussilicon layer.

SUMMARY

One disclosed embodiment of the present disclosure provides alight-emitting device including a transparent substrate having a firstsurface and a second surface opposite to the first surface; alight-emitting element on the first surface of the transparent substratethat emits light; and a porous layer on the second surface of thetransparent substrate, the porous layer including an organic materialand having pores, wherein the porous layer does not include inorganiccompound.

A comprehensive or specific embodiment may be provided using a member, asystem, or a method, or by any combination of a member, a device, asystem, and a method.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic, partial cross-sectional view of the structure ofa display device according to a first embodiment of the presentdisclosure.

FIG. 2 is a photomicrograph of a cross section of a porous layer and atransparent substrate in the display device according to the embodiment.

FIG. 3A schematically illustrates the state of reflection when thestructure of the display device according to the embodiment is used fora display device having a bottom-emission structure. FIG. 3Bschematically illustrates the state of reflection when the structure ofthe display device according to the embodiment is used for a displaydevice having a top-emission structure.

FIGS. 4A to 4D are partial cross-sectional views schematicallyillustrating some steps in a procedure for producing a display deviceaccording to the embodiment. FIG. 4A is a partial cross-sectional viewof a supporting substrate. FIG. 4B is a partial cross-sectional view ofa state in which a porous layer is formed on the supporting substrate.FIG. 4C is a partial cross-sectional view of a state in which atransparent substrate is formed on the porous layer. FIG. 4D is apartial cross-sectional view of a state in which a sealing layer isformed on the transparent substrate.

FIGS. 5A to 5C are partial cross-sectional views schematicallyillustrating some steps in the procedure for producing the displaydevice continued from FIG. 4D. FIG. 5A is a partial cross-sectional viewof a state in which an electrode layer is formed on the sealing layer.FIG. 5B is a partial cross-sectional view of a state in which athin-film transistor (TFT) main body layer is formed on the electrodelayer. FIG. 5C is a partial cross-sectional view of a state in which anorganic electroluminescent (EL) element layer is formed on the TFT mainbody layer.

FIGS. 6A and 6B are partial cross-sectional views schematicallyillustrating some steps in the procedure for producing the displaydevice continued from FIG. 5C. FIG. 6A is a schematic, partialcross-sectional view of the supporting substrate and the display devicein a state in which the porous layer is broken to separate thesupporting substrate. FIG. 6B is a partial cross-sectional viewschematically illustrating a state in which the display device accordingto the embodiment is completed.

FIG. 7 is a schematic flow chart of the procedure for producing thedisplay device according to the embodiment.

FIG. 8A is a partial cross-sectional view schematically illustrating astate in which a display device according to a second modification ofthe embodiment is formed on a supporting substrate. FIG. 8B is a partialcross-sectional view schematically illustrating the structure of thedisplay device according to the second modification of the embodiment.

FIGS. 9A to 9D are partial cross-sectional views schematicallyillustrating some steps in a procedure for producing the display deviceaccording to the second modification of the embodiment. FIG. 9A is apartial cross-sectional view schematically illustrating a state in whicha first porous sublayer is formed on a supporting substrate. FIG. 9B isa partial cross-sectional view schematically illustrating a state inwhich a second porous sublayer is formed on the first porous sublayer.FIG. 9C is a partial cross-sectional view schematically illustrating astate in which a transparent substrate is formed on the second poroussublayer. FIG. 9D is a partial cross-sectional view of the porous layerand the transparent substrate after the separation of the supportingsubstrate.

FIGS. 10A and 10B are partial cross-sectional views schematicallyillustrating some steps in a procedure for producing a display deviceaccording to an eighth modification of the embodiment. FIG. 10A is apartial cross-sectional view schematically illustrating a state in whicha porous layer is formed on a supporting substrate. FIG. 10B is apartial cross-sectional view schematically illustrating a state in whicha thin film is formed on the porous layer.

FIGS. 11A to 11C are partial cross-sectional views schematicallyillustrating some steps in the procedure for producing the displaydevice according to the eighth modification of the embodiment continuedfrom FIG. 10B. FIG. 11A is a partial cross-sectional view schematicallyillustrating a state in which the thin film is irradiated withultraviolet (UV) light. FIG. 11B is a partial cross-sectional viewschematically illustrating the state of the thin film after the UVirradiation. FIG. 11C is a partial cross-sectional view schematicallyillustrating a state in which a transparent substrate is formed on thethin film after the UV irradiation.

FIG. 12 is a schematic, partial cross-sectional view of the structure ofa display device not according to an embodiment of the presentdisclosure.

FIG. 13A schematically illustrates the state of reflection from adisplay device having a bottom-emission structure not according to anembodiment of the present disclosure. FIG. 13B schematically illustratesthe state of reflection from a display device having a top-emissionstructure not according to an embodiment of the present disclosure.

FIG. 14A is a partial cross-sectional view schematically illustrating astate in which an electronic device according to a second embodiment ofthe present disclosure is arranged on a supporting substrate. FIG. 14Bis a partial cross-sectional view schematically illustrating a state inwhich the electronic device according to the embodiment and thesupporting substrate illustrated in FIG. 14A are irradiated with laserlight.

FIG. 15 is a photomicrograph of a cross section of a porous layer and aplastic substrate of the electronic device according to the embodiment.

FIGS. 16A to 16D are partial cross-sectional views schematicallyillustrating some steps in a procedure for producing the electronicdevice according to the embodiment. FIG. 16A is a partialcross-sectional view of the supporting substrate. FIG. 16B is a partialcross-sectional view of a state in which the porous layer is formed onthe supporting substrate. FIG. 16C is a partial cross-sectional view ofa state in which the plastic substrate is formed on the porous layer.FIG. 16D is a partial cross-sectional view of a state in which a sealinglayer is formed on the plastic substrate.

FIGS. 17A to 17C are partial cross-sectional views schematicallyillustrating some steps in the procedure for producing the electronicdevice continued from FIG. 16D. FIG. 17A is a partial cross-sectionalview of a state in which an electrode layer is formed on the sealinglayer. FIG. 17B is a partial cross-sectional view of a state in which aTFT main body layer is formed on the electrode layer. FIG. 17C is apartial cross-sectional view of a state in which an organic EL elementlayer is formed on the TFT main body layer.

FIGS. 18A and 18B are partial cross-sectional views schematicallyillustrating some steps in the procedure for producing the electronicdevice continued from FIG. 17C. FIG. 18A is a partial cross-sectionalview schematically illustrating a state in which the electronic deviceand the supporting substrate are irradiated with laser light before theseparation of the supporting substrate. FIG. 18B is a partialcross-sectional view schematically illustrating the state of thesupporting substrate and the electronic device after the separation.

FIG. 19 is a schematic flow chart of the procedure for producing theelectronic device according to the embodiment.

FIG. 20A is a partial cross-sectional view schematically illustratingthe structure of test piece TP1. FIG. 20B is a partial cross-sectionalview schematically illustrating the structure of test piece TP2. FIG.20C is a partial cross-sectional view schematically illustrating thestructure of test piece TP3.

FIG. 21 illustrates the results of the evaluation of the effect ofsuppressing damage from laser irradiation by a method for producing anelectronic device according to the embodiment on damage suppression.

FIG. 22A is a photomicrograph of an electrode layer in an electronicdevice not according to the embodiment after laser irradiation. FIG. 22Bschematically illustrates a surface state of the electrode layerillustrated in FIG. 22A.

FIG. 23A is a photomicrograph of test piece TP1 after laser irradiation.FIG. 23B is a photomicrograph of test piece TP2 after laser irradiation.FIG. 23C is a photomicrograph of test piece TP3 after laser irradiation.

FIG. 24 is a graph of the measurement results of the amounts ofdisplacement of test pieces TP1, TP2, and TP3 after laser irradiation.

FIG. 25A is a partial cross-sectional view schematically illustrating astate in which an electronic device according to a first modification ofthe embodiment is arranged on a supporting substrate. FIG. 25B is apartial cross-sectional view schematically illustrating a state in whichan electronic device according to a second modification of theembodiment is arranged on a supporting substrate.

FIGS. 26A and 26B are partial cross-sectional views schematicallyillustrating some steps in a procedure for producing an electronicdevice according to a sixth modification of the embodiment. FIG. 26A isa partial cross-sectional view schematically illustrating a state inwhich a porous layer is formed on a supporting substrate. FIG. 26B is apartial cross-sectional view schematically illustrating a state in whicha thin film is formed on the porous layer.

FIGS. 27A to 27C are partial cross-sectional views schematicallyillustrating some steps in the procedure for producing the electronicdevice according to the sixth modification of the embodiment continuedfrom FIG. 26B. FIG. 27A is a partial cross-sectional view schematicallyillustrating a state in which the thin film is irradiated with UV light.FIG. 27B is a partial cross-sectional view schematically illustratingthe state of the thin film after the UV irradiation. FIG. 27C is apartial cross-sectional view schematically illustrating a state in whicha plastic substrate is formed on the thin film after the UV irradiation.

FIG. 28A is a partial cross-sectional view schematically illustrating astate in which an electronic device not according to the embodiment isarranged on a supporting substrate. FIG. 28B is a partialcross-sectional view schematically illustrating a state in which theelectronic device not according to the embodiment illustrated in FIG.28A and the supporting substrate are irradiated with laser light.

DETAILED DESCRIPTION Underlying Knowledge Forming Basis of the PresentDisclosure

In display devices, extraneous light (for example, light fromfluorescent lamps inside a building, and sunlight outside buildings) isreflected from screens, i.e., surfaces of displays, and observed asreflected images. This disadvantageously causes users to have difficultyin visually identifying display images on display surfaces. Moreover, indisplay devices having laminated structures, the problem with reflectioncan be caused by the structures in addition to the reflection ofextraneous light from display surfaces. That is, extraneous light thatenters display devices from display surfaces is reflected frominterfaces between layers or reflected from front or back surfaces ofone or more layers to emerge from display surfaces. The degree ofreflection of light depends on the angle of incidence and a differencein refractive index between substances located both sides of theinterfaces. Typically, a greater difference in refractive index resultsin a high degree of reflection. Thus, a higher degree of reflection isobtained at the interface between a solid layer and air, rather than theinterface between solid layers, such as a resin layer and a glass layer.Therefore, in general, the reflection of light from the front and backsurfaces, which are outermost surfaces, of a laminate is closely relatedto the problem with reflection.

FIG. 12 is a partial cross-sectional view schematically illustrating thestructure of a display device 500 serving as an organic EL displaydevice as a display device not according to an embodiment of the presentdisclosure. FIG. 13A schematically illustrates the state of formation ofreflected images when the structure of the display device 500 is usedfor a display device 500 a having a bottom-emission structure. FIG. 13Bschematically illustrates the state of formation of reflected imageswhen the structure of the display device 500 is used for a displaydevice 500 b having a top-emission structure.

As illustrated in FIG. 12, the display device 500 includes a sealinglayer 540, a TFT layer 550, and an organic EL element layer 560 stacked,in that order, on a transparent substrate 530. The transparent substrate530 is composed of a resin, such as an acrylic resin, or glass whichtransmits light. An interlayer insulating layer, a protective layer, andso forth may be arranged between the layers. A color filter, a sealinglayer, a protective layer, and so forth may be arranged on the organicEL element layer 560. The TFT layer 550 and the organic EL element layer560 constitute a display device element layer 570.

As illustrated in FIG. 13A, the display device 500 a, not according toan embodiment of the present disclosure, has a bottom-emissionstructure. In the case of the display device 500 a, extraneous light isreflected from a surface of the transparent substrate 530. The reflectedlight enters the eyes of a user together with light that expresses imageinformation, thereby forming reflected images. As illustrated in FIG.13B, the display device 500 b, not according to an embodiment of thepresent disclosure, has a top-emission structure. In the case of thedisplay device 500 b, part of extraneous light that enters the displaydevice 500 b from the organic EL element layer 560 is transmittedthrough the organic EL element layer 560, the TFT layer 550, the sealinglayer 540, and the transparent substrate 530 to reach the back surfaceof the transparent substrate 530. Then, the light is reflected from theback surface. The reflected extraneous light is again transmittedthrough the transparent substrate 530, the sealing layer 540, the TFTlayer 550, and the organic EL element layer 560 to enter the eyes of auser together with light that expresses image information, therebyforming reflected images. A main surface adjacent to a user is referredto as a “front surface”. A main surface remote from a user is referredto as a “back surface”. In the case of the display device 500 b, somecomponents of light that enters the display device 500 b are reflectedfrom the interfaces among the organic EL element layer 560, the TFTlayer 550, the sealing layer 540, and the transparent substrate 530.Other components of the light are reflected and absorbed by, forexample, electrodes (not illustrated) and wiring (not illustrated) inthe organic EL element layer 560 and the TFT layer 550. The reflectionand absorption occur for incident light and outgoing light. Thus,reflected light that forms reflected images is generally weak, comparedwith the case of the display device 500 a. Even in the case of thedisplay device 500 b, however, the reflection and absorption may be lesslikely to occur, depending on the angle of incidence of extraneous lightand a region of a display surface on which extraneous light is incident.As a result, strong reflected images may be formed, in some cases.Conventional light-emitting devices also have this reflection problem.

Accordingly, the inventors have conducted intensive studies in order toprovide a light-emitting device having satisfactory visibility bysuppressing reflection.

A light-emitting device according to an aspect of the present disclosureincludes a transparent substrate, a light-emitting element arranged onor above one main surface of the transparent substrate, and a porouslayer arranged on or above the other main surface of the transparentsubstrate, the porous layer being an organic material layer having aplurality of pores.

The porous layer is arranged on the main surface of the transparentsubstrate opposite to the side on which a light-emitting element lies.Thus, in the case where the light-emitting device has a bottom-emissionstructure, extraneous light incident on a front surface of thelight-emitting device, i.e., a main surface of the transparent substrateopposite to the side on which the light-emitting element lies, isscattered by the porous layer, thereby suppressing reflection. In thecase where the light-emitting device has a top-emission structure,extraneous light that enters the light-emitting device from a frontsurface of the light-emitting device is scattered by the porous layer atthe back surface serving as a main surface of the transparent substrateopposite to the side on which the light-emitting element lies. Thissuppresses the formation of reflected images due to the fact thatextraneous light that enters the light-emitting device is reflected fromthe back surface of the transparent substrate and emerges from the frontsurface of the light-emitting device.

The porous layer is formed of the organic material layer. Thus, unlikeporous inorganic material or inorganic particles, the following effectsare provided: The porous layer is formed of the organic material layer,thus resulting in excellent flexibility. The organic material layer iseasily curved at a low load. Thus, stress on the device element is lowupon applying a flexural load, so that the device element is less likelyto be damaged. Moreover, the porous layer is formed of the organicmaterial layer. It is thus possible to cushion an impact from theoutside to prevent the device from being damaged. Furthermore, since theporous layer is formed of the organic material layer, for example, inthe case where the device element is separated from the supportingsubstrate by laser irradiation during production, heat generated by thelaser irradiation is less likely to diffuse into the surroundings. Thus,the influence of heat on the device element is inhibited, and the energyof the laser is efficiently used to process the inorganic materiallayer. In addition, the porous layer is formed of the organic materiallayer and thus has heat insulation, so that it is possible to reduce theinfluence of external heat on the device element. As the organicmaterial layer, a porous polyimide film may be used.

The porous layer may not contain inorganic particles.

Inner surfaces of some pores among the plurality of pores may be exposedat a main surface of the porous layer opposite to a side on which thetransparent substrate lies. A gas may be present in the pores the innersurfaces of which are exposed.

In this case, when the light-emitting device has a bottom-emissionstructure, the main surface of the porous layer opposite to the side onwhich the transparent substrate lies serves as a display surface. Theirregularities formed by the exposure of the inner surfaces of somepores in the porous layer are present on the display surface. Thisscatters extraneous light at the display surface to suppress reflection.In addition, since extraneous light is scattered at the display surface,the entrance of extraneous light into the light-emitting device isinhibited. This suppresses the formation of reflected images due to thefact that extraneous light that enters the light-emitting device isreflected from the inside of the light-emitting device and emerges fromthe display surface, thereby enhancing the effect of suppressing theformation of reflected images.

The average diameter of the pores in a portion of the porous layeradjacent to the transparent substrate may be smaller than the averagediameter of the pores in a portion of the porous layer opposite to aside on which the transparent substrate lies.

In this case, when the light-emitting device has a top-emissionstructure, a higher degree of scattering of incident light occurs in aregion further away from the display surface, thereby suppressing theeffect of scattered light on display images.

In the porous layer, the average diameter of the pores in a first poroussublayer portion of the porous layer may be smaller than the averagediameter of the pores in a second porous sublayer portion of the porouslayer, the first porous sublayer portion including a main surface of theporous layer opposite to a side on which the transparent substrate lies,and the second porous sublayer portion being located at a positionnearer the transparent substrate than the first porous sublayer portion.

In the case where the light-emitting device has a bottom-emissionstructure, the inner surfaces of some pores in the porous layer areexposed at the display surface to form irregularities. The averagediameter of the pores in the first porous sublayer portion is smaller,thus resulting in smaller irregularities. This inhibits the degradationof the impression of the appearance and images to be displayed. Even inthe case of a touch-screen light-emitting device, it is possible toprovide a smooth operational feeling because of small irregularities onthe surface of the touch screen.

The light-emitting element may emit light to display an image toward thetransparent substrate, in which the porous layer may be composed of amaterial that transmits light.

In this case, when the light-emitting device according to an aspect ofthe present disclosure is used for a light-emitting device having abottom-emission structure, light that expresses image information istransmitted through the porous layer to reach the eyes of a user. Theporous layer scatters extraneous light to suppress the formation ofreflected images.

The porous layer may not contain inorganic particles.

A laminated substrate according to another aspect of the presentdisclosure includes a supporting substrate, a porous layer arranged onor above the supporting substrate, the porous layer being an organicmaterial layer and containing a plurality of pores in at least part of aregion of the porous layer, the plurality of pores containing internalspaces, and a gas being present in the internal spaces, and a resinsubstrate arranged on or above a main surface of the porous layeropposite to a side on which the supporting substrate lies.

In the structure of the laminated substrate according to anotherembodiment of the present disclosure, the at least part of the region ofthe porous layer contains the plurality of pores having internal spaces,so that the porous layer has lower stiffness than that of the resinsubstrate. For example, after an electronic device element and itscomponent are partially formed, the supporting substrate is separated byirradiation with laser light from the supporting substrate side. In thiscase, the energy of the pressure of a gas possibly generated from theresin substrate at the time of the laser light irradiation is consumedto break the porous layer. This reduces stress on the resin substrateand suppresses the deformation of the resin substrate, thus suppressingdamage to the electronic device element and so forth formed above theresin substrate.

The porous layer may not contain inorganic particles.

A method for producing a light-emitting device according to anotheraspect of the present disclosure includes preparing a supportingsubstrate, forming a porous layer on or above the supporting substrate,the porous layer being formed of an organic material layer andcontaining a plurality of pores, forming a transparent substrate on theporous layer, forming a light-emitting element on or above thetransparent substrate, breaking the porous layer at a portion inside theporous layer or an interface between the supporting substrate and theporous layer, and separating the supporting substrate from thetransparent substrate while at least part of the broken porous layer isattached to the transparent substrate.

In the method for producing a light-emitting device according to theanother aspect of the present disclosure, the porous layer is formed ona main surface of the transparent substrate opposite to the side onwhich the light-emitting element lies. The at least part of the porouslayer is attached to the main surface of the transparent substrateopposite to the side on which the light-emitting element lies. Thus, inthe case where the light-emitting device has a bottom-emissionstructure, a front surface of the light-emitting device, i.e., a mainsurface of the transparent substrate opposite to the side on which thelight-emitting element lies, is scattered by the porous layer, therebysuppressing reflection. In the case where the light-emitting device hasa top-emission structure, extraneous light that enters thelight-emitting device from a front surface of the light-emitting deviceis scattered by the porous layer at the back surface serving as a mainsurface of the transparent substrate opposite to the side on which thelight-emitting element lies. This suppresses the formation of reflectedimages due to the fact that extraneous light that enters thelight-emitting device is reflected from the back surface of thetransparent substrate and emerges from the front surface of thelight-emitting device.

The porous layer is formed of the organic material layer. Thus, unlikeporous inorganic material or inorganic particles, the following effectsare provided: The porous layer is formed of the organic material layer,thus resulting in excellent flexibility. The organic material layer iseasily curved at a low load. Thus, stress on the device element is lowupon applying a flexural load, so that the device element is less likelyto be damaged. Moreover, the porous layer is formed of the organicmaterial layer. It is thus possible to cushion an impact from theoutside to prevent the device from being damaged. Furthermore, since theporous layer is formed of the organic material layer, for example, inthe case where the device element is separated from the supportingsubstrate by laser irradiation during production, heat generated by thelaser irradiation is less likely to diffuse into the surroundings. Thus,the influence of heat on the device element is inhibited, and the energyof the laser is efficiently used to process the inorganic materiallayer. In addition, the porous layer is formed of the organic materiallayer and thus has heat insulation, so that it is possible to reduce theinfluence of external heat on the device element. As the organicmaterial layer, a porous polyimide film may be used.

The porous layer may not contain inorganic particles.

The break of the porous layer may be performed by irradiating the porouslayer with laser light from the supporting substrate side.

Thereby, it is possible to easily separate the supporting substrate withlaser light.

The break of the porous layer may be performed by applying mechanicalstress to the porous layer.

Thereby, it is possible to easily separate the supporting substrate witha roller or the like.

Some inner surfaces of the plurality of pores may be exposed at a mainsurface of the broken porous layer opposite to a side on which thetransparent substrate lies. A gas may be present in the pores the innersurfaces of which are exposed.

In this case, when the light-emitting device has a bottom-emissionstructure, the main surface of the porous layer opposite to the side onwhich the transparent substrate lies serves as a display surface. Theirregularities formed by the exposure of the inner surfaces of somepores in the porous layer are present on the display surface. Thisscatters extraneous light at the display surface to suppress reflection.In addition, since extraneous light is scattered at the display surface,the entrance of extraneous light into the light-emitting device isinhibited. This suppresses the formation of reflected images due to thefact that extraneous light that enters the light-emitting device isreflected from the inside of the light-emitting device and emerges fromthe display surface, thereby enhancing the effect of suppressing theformation of reflected images.

The average diameter of the pores in a portion of the porous layeradjacent to the transparent substrate may be smaller than the averagediameter of the pores in a portion of the porous layer opposite to aside on which the transparent substrate lies.

In this case, when the light-emitting device has a top-emissionstructure, a higher degree of scattering of incident light occurs in aregion further away from the display surface, thereby suppressing theeffect of scattered light on display images.

The average diameter of the pores in a first porous sublayer portion ofthe porous layer may be smaller than the average diameter of the poresin a second porous sublayer portion of the porous layer, the firstporous sublayer portion including a main surface of the porous layeropposite to a side on which the transparent substrate lies, and thesecond porous sublayer portion being located at a position nearer thetransparent substrate than the first porous sublayer portion.

In the case where the light-emitting device has a bottom-emissionstructure, the inner surfaces of some pores in the porous layer areexposed at the display surface to form irregularities. The averagediameter of the pores in the first porous sublayer portion is smaller,thus resulting in smaller irregularities. This inhibits the degradationof the impression of the appearance and images to be displayed. Even inthe case of a touch-screen light-emitting device, it is possible toprovide a smooth operational feeling because of small irregularities onthe surface of the touch screen.

The porous layer may contain the plurality of pores in at least part ofa region of the porous layer, the plurality of pores containing internalspaces, and a gas being present in the internal spaces. The transparentsubstrate may be a resin substrate. The supporting substrate may beseparated from the resin substrate by irradiation with laser light fromthe supporting substrate side.

In the production method, the at least part of the region of the porouslayer contains the plurality of pores having internal spaces, so thatthe porous layer has lower stiffness than that of the resin substrate.The energy of the pressure of a gas possibly generated from the resinsubstrate at the time of the laser light irradiation is consumed tobreak the porous layer. This reduces stress on the resin substrate andsuppresses the deformation of the resin substrate, thus suppressingdamage to the electronic device element formed above the resinsubstrate.

the average diameter of the pores in a portion of the porous layeradjacent to the resin substrate may be smaller than the average diameterof the pores in a portion of the porous layer adjacent to the supportingsubstrate.

Since the porous layer has the foregoing structure, when the resinsubstrate is formed on the porous layer, a resin material for the resinsubstrate is less likely to enter the pores the inner surfaces of whichare exposed at the main surface of the porous layer adjacent to theresin substrate. It is thus possible to maintain the internal spaces ofthe pores present in a surface layer portion on the side of the mainsurface and suppress an increase in the stiffness of the surface layerportion on the side of the main surface of the porous layer. Thisprevents the fact that the pressure of a gas generated at the time ofthe laser light irradiation causes difficulty in breaking the porouslayer. It is thus possible to maintain the effect of reducing stress onthe resin substrate.

The pressure of the gas generated by the laser light irradiation isreduced by breaking the porous layer. In addition, the pressure isreduced by the distribution of the pressure to the gas present in thepores in the porous layer. In particular, when a plurality of porescommunicate with each other, it is possible to obtain a higher effect ofdistributing pressure. Since the porous layer has the foregoingstructure, the internal spaces of the pores present in the surface layerportion on the side of the main surface of the porous layer aremaintained, thus maintaining the gas-pressure distributing effect.

The porous layer may include a first porous sublayer on the supportingsubstrate, and a second porous sublayer on the first porous sublayer, inwhich the average diameter of the pores in the second porous sublayermay be smaller than the average diameter of the pores in the firstporous sublayer.

In this case, a resin material for the resin substrate is less likely toenter the pores in the second porous sublayer located on the side onwhich the resin substrate is arranged. Thus, the internal spaces of thepores are maintained, thereby maintaining the effect of reducing stresson the resin substrate. Moreover, the effect of distributing thepressure of a gas generated at the time of laser light irradiation ismaintained. The first porous sublayer having the pores with an averagediameter larger than that of the second porous sublayer is arranged on aside of the second porous sublayer adjacent to the supporting substrate.This reduces the stiffness of the entire porous layer to suppress thedeformation of the resin substrate.

The second porous sublayer may be formed by a dry process or thermalevaporation.

In the case where the second porous sublayer is formed by a wet process,water and a solvent is left. This causes the generation of a gas at thetime of heating and laser irradiation in the subsequent productionprocess. Since the second porous sublayer is formed by a dry process orthermal evaporation, water and a solvent is not left, therebysuppressing the generation of a gas.

The first porous sublayer may be formed by the application of a firstresin material. The second porous sublayer may be formed by theapplication of a second resin material. The viscosity of the secondresin material may be higher than the viscosity of the first resinmaterial.

In this case, when the second porous sublayer is formed on the firstporous sublayer, the second resin material is less likely to enter thepores exposed at a main surface of the first porous sublayer on the sideon which the second porous sublayer is formed, thus maintaining theinternal spaces of the pores in the first porous sublayer. As a result,the entire porous layer has lower stiffness than that of the resinsubstrate.

In a state after the formation of the porous layer and before theformation of the resin substrate, some inner surfaces of the pluralityof pores may be exposed at a surface serving as a main surface of theporous layer on a side on which the resin substrate is to be formed.Moreover, after the formation of the porous layer and before theformation of the resin substrate, the porous layer may be subjected toaffinity treatment such that the affinity of the surface of the porouslayer for a resin material used to form the resin substrate is higherthan the affinity of a portion of the porous layer other than thesurface.

In this case, when the resin substrate is formed by the application ofthe resin material on the porous layer, the resin material is lesslikely to enter the inside the pores exposed at the main surface of theporous layer on the side on which the resin substrate is formed. Thus,the internal spaces of the pores in the porous layer are maintained,thereby maintaining the effect of reducing stress on the resinsubstrate. Moreover, the effect of distributing the pressure of a gasgenerated at the time of laser light irradiation is maintained.

In the affinity treatment, after a thin film of a material is formed onthe surface of the porous layer and the exposed inner surfaces, the UVlight irradiation or the plasma treatment may be performed from the sideon which the resin substrate is to be formed. The material have a loweraffinity for the resin material than that of a material used to form theporous layer, and have properties in which the affinity after UV lightirradiation or plasma treatment is higher than the affinity before theUV light irradiation or the plasma treatment.

The thin film may be formed by applying a solution containing a materialto the surface of the porous layer and the exposed inner surfaces andperforming drying. The material have a lower affinity for the resinmaterial than that of the material used to form the porous layer, andhave properties in which the affinity after UV light irradiation orplasma treatment is higher than the affinity before the UV lightirradiation or the plasma treatment.

In this case, the affinity treatment is easily performed.

The pores in the portion of the porous layer adjacent to the resinsubstrate may have an average diameter of 1 μm or less.

In this case, when the resin substrate is formed on the porous layer,the resin material is less likely to enter the pores exposed at the mainsurface of the porous layer on the side on which the resin substrate isformed. Thus, the internal spaces of the pores in the portion of theporous layer adjacent to the resin substrate are maintained, therebymaintaining the effect of reducing stress on the resin substrate.Moreover, the effect of distributing the pressure of a gas generated atthe time of laser light irradiation is maintained.

The pores in the second porous sublayer may have an average diameter of1 μm or less.

In this case, when the resin substrate is formed on the second poroussublayer, the resin material is less likely to enter the pores exposedat the main surface of the second porous sublayer on the side on whichthe resin substrate is formed. Thus, the internal spaces of the pores inthe portion of the second porous sublayer adjacent to the resinsubstrate are maintained, thereby maintaining the effect of reducingstress on the resin substrate. Moreover, the effect of distributing thepressure of a gas generated at the time of laser light irradiation ismaintained.

The porous layer may include a coating thin layer portion free from thepores, the coating thin layer portion being arranged on a surfaceserving as a main surface of the porous layer on a side on which theresin substrate is formed. The coating thin layer portion may becomposed of a material that is the same as that constituting a portionof the porous layer other than the coating thin layer portion.

In this case, when the resin substrate is formed on the porous layer,the resin material is blocked by the coating thin layer portion and doesnot enter the pores in the porous layer. Thus, the internal spaces ofthe pores in the porous layer are maintained, thereby maintaining theeffect of reducing stress on the resin substrate. Moreover, the effectof distributing the pressure of a gas generated at the time of laserlight irradiation is maintained. Furthermore, the coating thin layerportion is composed of a material that is the same as that constitutingthe portion of the porous layer other than the coating thin layerportion. Thus, increases in the number of steps and the types ofmaterials are suppressed, leading to the suppression of an increase inproduction cost.

The porous layer may not contain inorganic particles.

Embodiments and modifications of the present disclosure will bespecifically illustrated below. The structure, the effects, and theadvantages will be described.

The embodiments and the modifications described below are merelyexamples to clearly illustrate the structures according to an aspect ofthe present disclosure and the effects and advantages thereof. Thepresent disclosure is in no way limited to the following embodiments andmodifications, except for its inessential features.

First Embodiment

1. Structure of Display Device

The structure of a display device according to a first embodiment of thepresent disclosure will be described below with reference to FIGS. 1 and2 by taking, as an example, an active-matrix organic EL display devicefor which the structure is used.

FIG. 1 is a schematic, partial cross-sectional view of the structure ofa display device 100 according to this embodiment. In this embodiment,the display device 100 is an active-matrix organic EL display device.

As illustrated in FIG. 1, the display device 100 includes a porous layer20, a transparent substrate 30, a sealing layer 40, a TFT layer 50, andan organic EL element layer 60 stacked in that order. The TFT layer 50includes an electrode layer 51 and a TFT main body layer 52. The TFTlayer 50 and the organic EL element layer 60 constitute a display deviceelement layer (or a display device element) 70. The display device 100includes the display device element layer 70 above an upper surface (orone main surface) 31 of the transparent substrate 30 and the porouslayer 20 on a lower surface (or the other main surface) 32 of thetransparent substrate 30.

In FIG. 1, a figure in a circle drawn with a solid line is an enlargedcross-sectional view schematically illustrating the structure of aportion surrounded by a circle drawn with a broken line in thecross-sectional view of the display device 100 (specifically, a mainsurface and its vicinity of the porous layer 20 opposite to the side onwhich the transparent substrate 30 lies).

Porous Layer

As illustrated in the circle drawn with the solid line in FIG. 1 andFIG. 2, the porous layer 20 has many pores 21 therein. FIG. 2 is ascanning electron photomicrograph of a cross section of a portion in thevicinity of the interface between the porous layer 20 and thetransparent substrate 30. As illustrated in the figure in the circledrawn with the solid line in FIG. 1, inner surfaces 21 c of some of thepores 21 are exposed at a main surface 24 of the porous layer 20opposite the side on which the transparent substrate 30 lies. Air ispresent in the internal spaces of the pores 21 the inner surfaces 21 cof which are exposed.

In this embodiment, a gas, for example, air or a vaporized solvent, ispresent inside the pores 21, regardless of the pores the inner surfacesof which are exposed or not. A liquid, for example, water or a solvent,or solid foreign matter, such as dust, may be present in the internalspaces of the pores 21, in addition to the gas. For example, the pores21 may be filled with a material having a different refractive indexfrom a material for the porous layer 20. In this case, it is desirableto achieve a greater difference in refractive index between the materialwith which the internal spaces of the pores are filled and the materialfor the porous layer 20.

Here, the term “pores” are not limited to cell-like pores havingcompletely closed internal spaces and is used as a concept includingpores in which part of a cell-defining wall is absent, pores in which adefective portion of a wall is exposed at the outside, and pores inwhich the internal spaces of a plurality of cells communicate with eachother.

Furthermore, the term “pores” used here indicates pores each having adiameter of, for example, 10 nm or more and 10 μm or less, and desirably100 nm or more and 5 μm or less. In the case where a plurality of porescommunicate with each other, each of the pores may have a diameterwithin the above range.

Here, the diameter of each of the pores indicates the length of theinternal space of each pore in the direction to which a layer extends(i.e. direction perpendicular to the thickness direction of the layer).

Specifically, the porous layer 20 desirably has a porosity of, forexample, 10% or more and 90% or less.

More desirably, the porous layer 20 may have a porosity of 50% or moreand 90% or less. A porosity of 50% or more results in an increase in theproportion of the porous layer broken upon separating the supportingsubstrate with a laser, thereby resulting in a reduction in pressureapplied to the transparent substrate 30. At a porosity of 90% or less,the porous layer 20 ensures mechanical strength to a certain degree. Forexample, it is possible to suppress breakage due to mechanical stresscaused by, for example, a reduction or an increase in pressure at thetime of vacuum deposition in a production process. Specifically, thebreakage due to mechanical stress indicates the delamination of a filmand so forth. At an excessively high porosity, when the transparentsubstrate 30 is formed with a resin material (for example, polyimide),the resin material enters the pores, increasing the strength of theporous layer 20. Thus, the porous layer 20 desirably has a porosity ofabout 90% or less.

As a method for measuring the porosity of the porous layer 20, thefollowing method is employed: For example, a cross section of the porouslayer 20 is formed by mechanical cutting or focused ion beammicromachining. The cross section is observed with a scanning electronmicroscope. The ratio of pores at the cross section to the division walldefining the pores is calculated. It is easily assumed that a comparableratio is obtained in another cross section. Thus, the ratio isdetermined as a volume ratio and may be defined as the porosity.Furthermore, the measurement is performed at a plurality of points inthe cross section. It is possible to increase the accuracy by averagingthe resulting values of the porosity.

As the material for the porous layer 20, an organic material may beused.

Examples of a method for forming the porous layer 20 include, but arenot particularly limited to, a wet formation method and a dry formationmethod. A temperature during a step of forming the porous layer 20 or aheating temperature after the formation of the porous layer 20 isdesirably higher than a temperature in a step of forming each layerformed thereon. The reason for this is that when the steps of formingthe upper layers are performed at a higher temperature than theformation temperature of the porous layer 20, the porous layer 20 islikely to change, which is not desirable. For example, water, a solvent,and a gas adsorbed in the pores or on a solid portion of the porouslayer 20 may be desorbed at the time of the formation steps of the upperlayers, causing a failure, such as separation from the upper layer.

The thickness of the porous layer 20 is desirably, but not particularlylimited to, about 1 μm to about 1000 μm.

Transparent Substrate

Examples of a material for the transparent substrate 30 include, but arenot particularly limited to, glass materials, such as alkali-free glass(borosilicate glass), alkali glass, soda glass, non-fluorescent glass,phosphate-based glass, borate glass, and silica; insulating materials,such as alumina; and resin materials, such as polyethylene,polypropylene, polyvinylene, polyvinylidene chloride, polyethyleneterephthalate, polyethylene naphthalate, polycarbonate, polyethylenesulfonic acid, silicone, acrylic resins, epoxy resins, phenolic resins,polyamide, polyimide, and aramid resins. These materials may be used incombination as a mixture of two or more thereof. These materials may bechemically modified. Two or more of these materials may be combined toform a multilayer structure.

In the case where the display device 100 is a flexible display, thetransparent substrate 30 is required to have the characteristics inwhich the transparent substrate 30 is not easily cracked or broken whencurved. If the transparent substrate 30 does not have thecharacteristics, it is impossible to provide a display device with highflexibility.

In the case where the display device 100 is a flexible display, thethickness of the transparent substrate 30 is desirably in the range of 1μm to 1000 μm. At a thickness smaller than the range, mechanicalstrength is not ensured. At a thickness larger than the range, thesubstrate is difficult to bend, thus failing to provide a display devicewith high flexibility.

Regarding a method for forming the transparent substrate 30, in the casewhere the transparent substrate is a resin material, the transparentsubstrate 30 may be formed by the application of a liquid resinmaterial. In the case where the transparent substrate 30 is composed ofa material, for example, a resin or glass, a plate- or film-shapedmaterial may be bonded to the porous layer 20, without any limitation.When a plate- or film-shaped material is bonded, the bonding may beperformed with an adhesive or the like or by pressure bonding. Theadhesive is not particularly limited as long as a desired adhesive forceis provided. Examples thereof include silicone-based adhesives andacrylic-based adhesives. The transparent substrate 30 may be a plasticsubstrate 330 described below.

Sealing Layer

The sealing layer 40 may be formed of, for example, a silicon nitridefilm.

TFT Layer

The TFT layer 50 includes a TFT configured to drive an organic ELelement. The TFT layer 50 includes the electrode layer 51 formed of agate electrode included in the TFT, and the TFT main body layer 52constituting a portion of the TFT except the gate electrode.

The electrode layer 51 is formed by depositing a metal material by avacuum evaporation method or a sputtering method and selectivelyremoving the resulting metal material film by, for example, etching.Examples of a material for the electrode layer 51 include silver,aluminum, alloys of silver, palladium, and copper, and alloys of silver,rubidium, and gold.

The TFT main body layer 52 includes, for example, a gate-insulatingfilm, source-drain electrodes, a bank, a semiconductor layer, and apassivation film. Examples of the TFT that may be used include a TFTwhose channel material is silicon, a TFT whose channel material is anoxide semiconductor, such as an indium-gallium-zinc oxide, and a TFTwhose channel material is an organic semiconductor, such as pentacene.

Organic EL Element Layer

The organic EL element layer 60 includes an upper electrode, a lowerelectrode, and an organic functional layer arranged between the upperelectrode and the lower electrode. The organic functional layer includesa light-emitting layer. The organic functional layer may appropriatelyinclude an electron injection layer, an electron transport layer, a holeinjection layer, a hole transport layer, and other layer, in addition tothe light-emitting layer. The organic EL element layer 60 may include apartition layer, a sealing layer, and so forth, in addition to the upperelectrode, the lower electrode, and the organic functional layer. Theorganic EL element layer 60 may further include a color filter and aprotective filter.

The TFT layer 50 and the organic EL element layer 60 constitute thedisplay device element layer 70.

In this embodiment, the TFT layer 50 has a multilayer structureincluding the electrode layer 51 and the TFT main body layer 52.However, the TFT layer 50 is not limited to the structure. For example,in the case where the display device 100 is a passive-matrix organic ELdisplay device, a wiring layer corresponds to the TFT layer 50.

In the case where the display device 100 is a liquid crystal displaydevice, LCD elements are arranged in the display device element layer70.

2. Suppression of Reflection

FIG. 3A is a partial cross-sectional view schematically illustrating thestate of suppression of the formation of reflected images when thestructure of the display device 100 according to this embodiment is usedfor a display device 100 a having a bottom-emission structure. FIG. 3Bis a partial cross-sectional view schematically illustrating the stateof suppression of the formation of reflected images when the structureof the display device 100 according to this embodiment is used for adisplay device 100 b having a top-emission structure.

In the case of the display device 100 a having a bottom-emissionstructure illustrated in FIG. 3A, light that expresses image informationemitted from the light-emitting layer in the organic EL element layer 60is transmitted through the TFT layer 50, the sealing layer 40, thetransparent substrate 30, and the porous layer 20 to enter the eyes of auser. In this case, the porous layer 20 is composed of a material thattransmits light.

Meanwhile, extraneous light is reflected from a surface of the porouslayer 20 (i.e. a main surface of the porous layer 20 opposite to theside on which the transparent substrate 30 lies) and enters the eyes ofthe user together with light that expresses image information. This isrecognized by the user as reflected images, causing a reduction in thevisibility of the image information. However, as illustrated in thecircle drawn by the solid line of FIG. 1, the inner surfaces 21 c ofsome pores 21 in the porous layer 20 are exposed at the surface of theporous layer 20 to form irregularities. This scatters extraneous lightat the surface of the porous layer 20 to reduce reflected light thatenters the eyes of the user, thereby suppressing the formation ofreflected images. Furthermore, extraneous light passes through thesurface of the porous layer 20 and enters the porous layer 20 is alsoscattered by refraction and reflection when passes through theinterfaces between the solid portion of the porous layer 20 and the gasportions inside the pores 21 in the porous layer 20. Thus, extraneouslight that passes through the porous layer 20 and is incident on thetransparent substrate 30 is reduced. This reduces reflection from theinterface between the transparent substrate 30 and the sealing layer 40,reflection from the interface between the sealing layer 40 and thedisplay device element layer 70, reflection from the interfaces betweenthe layers constituting the display device element layer 70, andreflection from the surfaces of components, such as electrodes, therebyfurther suppressing the formation of reflected images.

As illustrated in FIG. 2, the porous layer 20 includes a coating thinlayer portion 22 on the surface of the porous layer 20 adjacent to thetransparent substrate 30, the coating thin layer portion 22 having athickness of about 1 μm and being free from a pore. Thus, when the resinmaterial is applied to the porous layer 20 to form the transparentsubstrate 30, the resin material does not enter the pores, so that theinternal spaces of the pores are not filled with the resin material.Thus, the internal spaces of the pores in the porous layer 20 aremaintained, thereby advantageously maintaining a large amount of lightscattered.

In the case of the display device 100 b having a top-emission structure,light emitted from the organic functional layer in the organic ELelement layer 60 emerges from the upper surface of the organic ELelement layer 60, i.e., is emitted to the outside through the upperelectrode. Thus, the upper electrode composed of a material thattransmits light (i.e. transparent conductive film) is used. In recentyears, in the case of a transparent display, a material withsatisfactory optical transparency has often been used for the lowerelectrode and the TFT layer 50. Thus, extraneous light that enters thedisplay device 100 b from the outgoing light side of the organic ELelement layer 60, i.e., from the side of a user, enters the porous layer20 through the organic EL element layer 60, the TFT layer 50, thesealing layer 40, and the transparent substrate 30. The light thatenters the porous layer 20 reaches the back surface of the porous layer20 (i.e. a main surface of the porous layer 20 opposite to the sideadjacent to the user, and here, the main surface of the porous layer 20opposite the side on which the transparent substrate 30 lies). Air,which is in a gaseous state, is present outside the porous layer 20,which is in a solid state. Thus, extraneous light seems easily reflectedfrom the back surface, which is the interface therebetween, of theporous layer 20. The inner surfaces 21 c of some pores 21 in the porouslayer 20 are exposed at the back surface of the porous layer 20 to formirregularities, as illustrated in the circle drawn by the solid line inFIG. 1. Thus, the extraneous light that reaches the back surface of theporous layer 20 through the layers in the display device 100 b isscattered at the back surface of the porous layer 20, thereby reducingthe reflection of the extraneous light at the back surface. This reducesthe extraneous light that is reflected from the back surface of theporous layer 20 and passes again through the layers in the displaydevice 100 b to enter the eyes of the user, thereby suppressing theformation of reflected images.

In the case of a display device 500 b having a top-emission structureillustrated in FIG. 13B not according to this embodiment, light that isobliquely incident on the display device from the outside is easilyreflected from components in the display device element layer 570 anddoes not easily reach the back surface of the transparent substrate 530.Similarly, light that is reflected from the back surface of thetransparent substrate 530 is also reflected from components in thedisplay device element layer 570 and is not easily emitted to a user.Thus, in the case where the display device having a top-emissionstructure is used, the amount of light that is reflected from the backsurface of the transparent substrate 530 to be emitted toward the useris small.

However, light vertically incident on a display surface of the displaydevice (in the display device 500 b, a main surface of the organic ELelement layer 560 adjacent to the user), specifically, light incident ona transparent region, such as an interpixel region, is reflected. Inthis case, the reflected light may be emitted to the user. This mayadversely affect the visibility of an image, as with the bottom-emissionstructure.

Even in such a case, in the display device 100 b having a top-emissionstructure for which the structure of the display device 100 according tothis embodiment is used, it is possible to suppress the formation ofreflected images as described above.

In the case of a display device including a flat glass substrate notaccording to this embodiment, requirements for the formation ofreflected images are circumvented by slightly tilting the angle of thedisplay device. Thus, the visibility is relatively easily improved.

In contrast, in the case of a flexible display device in which aflexible material, such as a resin substrate, is used for a substrateand the display device can be used in a curved state, the angle ofreflection from a display surface is continuously present with respectto a user. Thus, even if the angle is adjusted, a point having an anglethat forms reflected images is changed. It is difficult to adjust theangle that completely circumvents requirements for the formation ofreflected images. Accordingly, in particular, in the case of a flexibledisplay device having a curved display, it is particularly importantthat the reflection of light from the back surface side of thetransparent substrate should be suppressed.

Even in this case, in the display device 100 b having a top-emissionstructure for which the structure of the display device 100 according tothis embodiment is used, it is possible to effectively suppress theformation of reflected images as described above.

As illustrated in FIG. 2, in the porous layer 20 according to thisembodiment, the diameters of pores 21 a in a portion near thetransparent substrate 30 are generally smaller than those of pores 21 bin a portion further away from the transparent substrate 30. In otherwords, the average diameter of the pores 21 a is smaller than theaverage diameter of the pores 21 b. The term “average diameter” may berepresented by an average diameter obtained in an area of 10×10 μm². Forexample, the average diameter may be represented by an average diameterobtained by the observation of two or three points in a cross section ofthe porous layer 20 with a focused ion beam (FIB) scanning electronmicroscope (SEM).

In the case of a display device having a top-emission structure,incident light that would not reflected in the direction to the eyes ofa user if the porous layer 20 were not provided may be scattered at theporous layer 20 to reach the eyes of the user.

If the average diameter of the pores 21 in a portion near thetransparent substrate 30 is larger, the number of the pores 21 per unitvolume is small in the portion near the transparent substrate 30. Thus,the number of refractions and reflections of incident light is small inthe portion. For this reason, the incident light is less scattered andis reflected to the user side while the intensity of light remains high,in some cases.

However, in the display device 100 according to this embodiment, asdescribed above, the average diameter of the pores 21 a in a portion ofthe porous layer 20 near the transparent substrate 30 is smaller thanthe average diameter of the pores 21 b in a portion of the porous layer20 further away from the transparent substrate 30. Thus, the number ofthe pores 21 per unit volume in the portion near the transparentsubstrate 30 is larger than that in the portion further away from thetransparent substrate 30. Hence, the number of refractions andreflections of incident light is large in the portion near thetransparent substrate 30, thereby more uniformly scattering the incidentlight. As a result, when the incident light is reflected in the portionnear the transparent substrate 30 to the user side, the reflected lightis weakened by the scattering. It is thereby possible to suppress theinfluence of light reflected from the porous layer 20.

In the case of a display device having a bottom-emission structure, thepores 21 a in the portion of the porous layer 20 near the transparentsubstrate 30 have a small average diameter, and the porous layer 20contains the pores with different average diameters; hence, it ispossible to scatter light in a wider wavelength range. This results inthe effect of effectively scattering all visible light.

3. Method for Producing Display Device

A method for producing the display device 100 according to thisembodiment will be described below with reference to FIGS. 4A to 4D, 5Ato 5C, 6A and 6B, and 7. FIGS. 4A to 4D, 5A to 5C, and 6A and 6B arepartial cross-sectional views schematically illustrating some steps in aprocedure for producing the display device 100 according to thisembodiment. FIG. 7 is a schematic flow chart of the procedure forproducing the display device 100 according to this embodiment.

As illustrated in FIG. 4A, a supporting substrate 10 is prepared (stepS1 in FIG. 7). The supporting substrate 10, on which the display device100 is to be formed, is a member serving as a base used for theformation of the display device 100.

Examples of a material for the supporting substrate 10 include, but arenot particularly limited to, glass materials, such as alkali-free glass(borosilicate glass), alkali glass, soda glass, non-fluorescent glass,phosphate-based glass, borate glass, and silica; and insulatingmaterials, such as alumina. In this embodiment, a specific example ofthe supporting substrate 10 is EAzLE 2000, manufactured by CorningIncorporated.

A surface of the supporting substrate 10 (a main surface of thesupporting substrate 10 on the side on which the display device 100 isto be formed) desirably has a high degree of flatness because athin-film device element, such as a display device element, is formedafter the temporal fixation of the transparent substrate 30.Specifically, the surface has a maximum level difference of 10 μm orless and desirably 1 μm or less.

The surface of the supporting substrate 10 is desirably in a clean statein order to achieve good adhesion to a layer to be formed thereon. As amethod for cleaning the surface, for example, UV light irradiation,ozone treatment, plasma treatment, or hydrofluoric acid treatment may beemployed. In this embodiment, specifically, for example, the supportingsubstrate 10 is subjected to excimer UV (wavelength: 172 nm) treatmentto clean the surface.

A single layer configured to improve adhesion to a layer to be formedthereon may be formed on a surface of the supporting substrate 10. Asthe layer configured to improve adhesion, for example, a silicon oxidefilm may be used.

As illustrated in FIG. 4B, the porous layer 20 is formed on thesupporting substrate 10 (step S2 in FIG. 7). In this embodiment,specifically, for example, a polyimide is applied to the supportingsubstrate 10 by a spin coating method. The applied polyimide is heatedat a heating temperature of 400° C. for 8 hours, thereby forming an18-μm-thick porous polyimide layer serving as the porous layer 20. Aspecific example of the polyimide used as a material for the porouslayer 20 is U Imide Varnish Type BP manufactured by Unitika Limited.

As illustrated in FIG. 4C, the transparent substrate 30 serving as asubstrate for a flexible display is formed on the porous layer 20 (stepS3 in FIG. 7). In this embodiment, specifically, for example, apolyimide layer having a thickness of 30 μm is formed by a spin coatingmethod on the porous layer 20, thereby forming the transparent substrate30 serving as a substrate for a flexible display. A specific example ofthe polyimide used as a material for the transparent substrate 30 isU-Varnish manufactured by Ube Industries, Ltd.

As illustrated in FIG. 4D, the sealing layer 40 is formed on thetransparent substrate 30 (step S4 in FIG. 7). In this embodiment,specifically, for example, a 1-μm-thick silicon nitride film serving asthe sealing layer 40 is formed by capacitively coupled plasma-enhancedchemical vapor deposition (CVD) at 300° C.

As illustrated in FIG. 5A, a thin metal film is formed on the sealinglayer 40 and then is subjected to etching treatment, thereby forming theelectrode layer 51 (step S5 in FIG. 7). In this embodiment,specifically, for example, a 100-nm-thick layer composed of an alloy ofmolybdenum and tungsten is formed by a sputtering method. The layer ispatterned by a photolithography method with a resist and then subjectedto etching treatment with a liquid mixture of phosphoric acid, nitricacid, and acetic acid, thereby forming the electrode layer 51.

As illustrated in FIG. 5B, the TFT main body layer 52 is formed on theelectrode layer 51, thereby completing the TFT layer 50 (step S6 in FIG.7).

As illustrated in FIG. 5C, the organic EL element layer 60 is formed onthe TFT layer 50 (step S7 in FIG. 7), thereby providing an electrondevice body 1000 in which the display device 100 is formed on thesupporting substrate 10.

As illustrated in FIG. 6A, the porous layer 20 is broken at a portion inthe porous layer 20 to separate the transparent substrate 30 from thesupporting substrate 10 (step S8 in FIG. 7), thereby providing thedisplay device 100 as illustrated in FIG. 6B.

For the separation of the supporting substrate 10, the following methodmay be employed: a method in which the electron device body 1000 isirradiated with laser light from the supporting substrate 10 side, or amethod in which mechanical separation is performed with a roller. Inthis embodiment, specifically, for example, the supporting substrate 10is separated by irradiation with excimer laser light having a wavelengthof 305 nm, a pulse width per pulse of 20 ns, an irradiation area of 20.0mm×1.0 mm from the supporting substrate 10 side while the excimer laserlight is swept.

This embodiment is not limited to the state in which the porous layer 20is broken at a portion in the porous layer 20 to separate the supportingsubstrate 10 and part of the porous layer 20 is attached to thetransparent substrate 30, as illustrated in FIG. 6A. When the supportingsubstrate 10 is separated from the porous layer 20 at the interfacebetween the porous layer 20 and the supporting substrate 10, the entireporous layer 20 may be attached to the transparent substrate 30. Inother words, at least part of the porous layer 20 may be attached to thetransparent substrate 30 after the separation of the supportingsubstrate 10. In this case, however, it is desirable that a main surfaceof the transparent substrate 30 opposite to the side on which thesealing layer 40 lies be completely covered with the porous layer 20. Ifthe main surface is not completely covered, at least a regioncorresponding to an image display region is desirably covered with theporous layer 20.

In the display device 100 according to this embodiment, as illustratedin FIG. 2, the average diameter of the pores 21 a in the portion of theporous layer 20 near the transparent substrate 30 is smaller than theaverage diameter of the pores 21 b in the portion of the porous layer 20further away from the transparent substrate 30. This reducesirregularities on an upper surface of the porous layer 20 (i.e. a mainsurface of the porous layer 20 on the side on which the transparentsubstrate 30 is formed) and reduces the influence of the irregularitieson the layers formed on and above the porous layer 20, thereby providinga higher-quality display device.

Specifically, the average diameter of the pores in the portion of theporous layer 20 adjacent to the transparent substrate 30 is desirably,for example, 10 nm or more and 100 nm or less. Specifically, the averagediameter of the pores in the portion of the porous layer 20 adjacent tothe supporting substrate 10 is desirably, for example, 100 nm or moreand 10 μm or less.

To solve the problem of the formation of reflected images, a method isconceivable in which a filler is dispersed in the transparent substrateto suppress the reflection of incident light. In this case, however,irregularities are formed on an upper surface of the transparentsubstrate by the influence of the filler. As a result, the sealingperformance of the sealing layer 40 formed thereon is disadvantageouslyreduced. The structure of the display device 100 according to thisembodiment suppresses the formation of reflected images without reducingthe sealing performance of the sealing layer 40.

In the case where a polarizing film is used in order to suppress theformation of reflected images, particularly in the case of abottom-emission structure, light that expresses image information isalso changed. The amount of light that enters the eyes of a user isreduced, disadvantageously significantly reducing the brightness of adisplay screen. The structure of the display device 100 according tothis embodiment suppresses the formation of reflected images without asignificant reduction in the brightness of the display screen.

Modification

While the present disclosure has been described on the basis of theembodiment, the present disclosure is not limited to the foregoingembodiment. The following modifications may be performed.

First Modification

In the foregoing embodiment, the porous layer 20 includes the coatingthin layer portion 22. However, the porous layer 20 is not limitedthereto. The porous layer 20 may have a structure free from the coatingthin layer portion 22.

In this case, the average diameter of the pores in a portion of theporous layer 20 adjacent to the transparent substrate 30 is desirablysmaller than the average diameter of the pores in a portion of theporous layer 20 adjacent to the supporting substrate. In the case of asmaller average diameter of the portion of the porous layer 20 adjacentto the transparent substrate 30, when the transparent substrate 30 isformed by application with a resin material, the resin material is lesslikely to enter the pores. Thus, the internal spaces are maintained,thereby maintaining the effect of scattering light in the portion of theporous layer 20 near the transparent substrate 30.

In the foregoing embodiment, the porous layer 20 is formed by applying aresin material and then heating the applied resin material. In general,bubbles of a solvent disappear more easily at a position closer to asurface. Thus, the pores closer to the surface have a smaller averagediameter. The heating temperature, the heating time, and the type andamount of the solvent in the resin material at the time of the formationof the porous layer 20 may be adjusted in such a manner that the coatingthin layer portion 22 is not formed.

Second Modification

In the display device 100 according to the foregoing embodiment, whilethe porous layer 20 has a single-layer structure, the porous layer 20 isnot limited thereto. The porous layer 20 may have a multilayer structureincluding a plurality of sublayers.

FIG. 8A is a partial cross-sectional view schematically illustrating anelectron device body 2000 in which a display device 200 according to asecond modification is arranged on the supporting substrate 10. FIG. 8Bis a partial cross-sectional view schematically illustrating thestructure of the display device 200.

As illustrated in FIGS. 8A and 8B, the display device 200 includes theporous layer 220. The porous layer 220 includes two sublayers: a firstporous sublayer 220 a and a second porous sublayer 220 b.

FIGS. 9A to 9D are partial cross-sectional views schematicallyillustrating some steps in a procedure for producing the display device200. FIG. 9A is a partial cross-sectional view schematicallyillustrating a state in which the first porous sublayer (first poroussublayer portion) 220 a is formed on the supporting substrate 10. FIG.9B is a partial cross-sectional view schematically illustrating a statein which the second porous sublayer (second porous sublayer portion) 220b is formed on the first porous sublayer 220 a. FIG. 9C is a partialcross-sectional view schematically illustrating a state in which thetransparent substrate 30 is formed on the second porous sublayer 220 b.FIG. 9D is a partial cross-sectional view of the porous layer 220 andthe transparent substrate 30 of the display device 200 after theseparation of the supporting substrate 10. In FIG. 9D, the sealing layer40, the TFT layer 50, and the organic EL element layer 60 are notillustrated.

As illustrated in FIGS. 9B, 9C, and 9D, in the display device 200according to the second modification, the average diameter of pores inthe first porous sublayer 220 a is smaller than the average diameter ofpores in the second porous sublayer 220 b.

As described in the first modification, in the case where the porouslayer is formed by applying a resin material and then heating theapplied resin material, in general, the average diameter of the pores issmaller in a portion closer to a surface.

In the case where a single porous layer is formed as in the displaydevice 100 according to the foregoing embodiment, if the pores in theporous layer 20 have an excessively small average diameter, alow-porosity portion having a very small diameter and a pore-freeportion in which pores disappear are formed in the vicinity of thesurface. In particular, when the structure is used for a display devicehaving a top-emission structure, the effect of sufficiently scatteringlight is less likely to be provided.

In the case where the pores in the porous layer 20 have a large averagediameter, in particular, in the case of a display device having abottom-emission structure, a portion of the porous layer 20 in closecontact with the supporting substrate 10, i.e., a portion where thepores have large diameters, is exposed on the user side. In this case,an excessively large diameter of the pores can cause irregularities onthe display surface to increase, thereby degrading the impression of theappearance and images to be displayed. In the case where a displayfunctions also as a touch screen, the touch is not smooth when a usertouches it with a finger, thus possibly failing to provide asatisfactory operational feeling.

In the display device 200 according to the second modification, theporous layer 220 includes the first porous sublayer 220 a and the secondporous sublayer 220 b arranged on the first porous sublayer 220 a. Theaverage diameter of the pores in the first porous sublayer 220 a issmaller than the average diameter of the pores in the second poroussublayer 220 b. Thus, even in the case where the display device 200 isused for a display device having a top-emission structure, the pores inthe second porous sublayer 220 b adjacent to the transparent substrate30 have a larger average diameter; hence, the porosity is ensured toprovide the effect of sufficiently scattering light. In the case wherethe display device 200 is used for a display device having abottom-emission structure, as illustrated in FIG. 9D, the first poroussublayer 220 a that contains the pores having a small average diameteris exposed on the user side, thereby resulting in a display surfacehaving smaller irregularities. This inhibits the degradation of theimpression of the appearance and images to be displayed. In addition,even in the case of a touch-screen display device, it is possible toprovide a smooth operational feeling because of small irregularities onthe surface of the touch screen.

As with the porous layer 220 according to the second modification, theaverage diameter of the pores in a portion of the porous layer 220opposite to the side adjacent to the transparent substrate 30 (in thiscase, the first porous sublayer 220 a) may be smaller than the averagediameter of the pores at a predetermined position in the porous layer220 in the thickness direction (in this case, a portion of the secondporous sublayer 220 b adjacent to the first porous sublayer 220 a).

In the second modification, the porous layer 220 includes the twosublayers. However, the porous layer 220 is not limited thereto. Theporous layer 220 may include three or more sublayers.

Third Modification

In the second modification, the second resin material for the formationof the second porous sublayer 220 b desirably has a higher viscositythan that of the first resin material for the formation of the firstporous sublayer 220 a. In this case, the second resin material for theformation of the second porous sublayer 220 b is less likely to enterthe pores in the first porous sublayer 220 a, thereby maintaining theporosity of the first porous sublayer 220 a.

Fourth Modification

In the second modification, the case where the average diameter of thepores in the first porous sublayer 220 a is smaller than the averagediameter of the pores in the second porous sublayer 220 b has beendescribed. However, the present disclosure is not limited thereto. Theaverage diameter of the pores in the first porous sublayer 220 a may belarger than the average diameter of the pores in the second poroussublayer 220 b.

In this case, the effect of scattering light is enhanced in the firstporous sublayer 220 a containing the pores having a larger averagediameter. Thus, incident light is markedly scattered at a region furtheraway from a surface from which light that expresses image informationemerges (here, the light-emitting layer in the organic EL element layer60), thereby suppressing the influence of the scattered light on adisplay image.

Fifth Modification

In the case where the porous layer 220 includes the first poroussublayer 220 a and the second porous sublayer 220 b as with the secondmodification, the second porous sublayer 220 b may be formed by any oneof dry processes selected from a chemical vapor deposition method, asputtering method, and an evaporation method. When the second poroussublayer 220 b is formed by a wet process, water and a solvent are leftin the pores and a solid portion of the second porous sublayer 220 b.Thus, in the cases where a subsequent heating step is performed andwhere laser irradiation is performed for the separation of thesupporting substrate 10 in the production process, water and the solventcause the generation of gases. In the case where the second poroussublayer 220 b is formed by a dry process or thermal evaporation, waterand a solvent are not left, thereby inhibiting the generation of a gas.

Sixth Modification

In the case where the transparent substrate 30 is bonded to the porouslayer 20, an adhesive layer may be provided between the porous layer 20and the transparent substrate 30. The adhesive layer is typically formedby application. Thus, when the pores in a surface portion of the porouslayer 20 on the side on which the transparent substrate 30 is formedhave a smaller average diameter, a material constituting the adhesivelayer is less likely to penetrate into the pores. Also in the case ofthe bonding, when the pores in the surface portion of the porous layer20 on the side on which the transparent substrate 30 is formed have asmaller average diameter, a larger area of a surface of the porous layer20 in close contact with the transparent substrate 30 is provided,compared with the case of a large average diameter, thereby increasingthe adhesion to the transparent substrate 30. This prevents accidentaldetachment of the transparent substrate 30 from the porous layer 20 inthe course of the production process of the display device.

Seventh Modification

The pores present in a portion of the porous layer 20 in the vicinity ofa main surface of the porous layer 20 adjacent to the transparentsubstrate 30 may be filled with a resin material for the transparentsubstrate 30, and the pores in a portion of the porous layer 20 oppositethe side on which the transparent substrate 30 lies may contain a gasand may have internal spaces. When the pores have the internal spaces, agreater difference in refractive index is achieved at the time of thepassage of light through the inner surfaces of the pores, therebyincreasing the scattering of light. By filling the pores in the portionadjacent to the transparent substrate 30 with the resin material andmaintaining the unfilled pores in the portion remote from thetransparent substrate 30, incident light is markedly scattered at aregion further away from a surface from which light that expresses imageinformation emerges. In this case, the light that expresses imageinformation emerges from the surface of the light-emitting layer in theorganic EL element layer 60. Thereby, the influence of the scatteredlight on a display image is suppressed.

Eighth Modification

In the case where the transparent substrate 30 is formed by theapplication of a resin material, affinity treatment may be performedafter a step of forming the porous layer 20 and before a step of formingthe transparent substrate 30. The affinity treatment may be performedsuch that the affinity of a surface 23 of the porous layer 20 (i.e. amain surface of the porous layer 20 on the side on which the transparentsubstrate 30 is to be formed) for the resin material used to form thetransparent substrate 30 (hereinafter, referred to simply as “resinaffinity”) is higher than the resin affinity of the inner surfaces 21 cof the pores 21 exposed at the surface 23.

A method of the affinity treatment will be described below withreference to FIGS. 10A to 11C.

FIG. 10A is a partial cross-sectional view illustrating a state in whichthe porous layer 20 is formed on the supporting substrate 10. Asillustrated in the figure, the inner surfaces 21 c of some pores 21 areexposed at the surface 23 of the porous layer 20.

As illustrated in FIG. 10B, a thin film 90 having a low resin affinityis formed on the surface 23 and the inner surfaces 21 c. The thin film90 may be formed by, for example, applying a solution containing amaterial having a low resin affinity to the surface 23 and the innersurfaces 21 c and then performing drying.

As illustrated in FIG. 11A, the thin film 90 is irradiated with UVlight. Thereby, as illustrated in FIG. 11B, a portion of the thin film90 formed on the surface 23 of the porous layer 20, portions of the thinfilm 90 formed on shallow portions of the inner surfaces 21 c of thepores 21, and portions of the thin film 90 formed on regionscorresponding to bottoms of wide openings are exposed to the UV light toincrease the resin affinity, resulting in high-resin-affinity portions90 a. A sufficient amount of UV light does not reach portions of thethin film 90 formed on deep portions of the inner surfaces 21 c of thepores 21 and inclined portions of the thin film 90 substantiallyparallel to the irradiation direction of the UV light and being formednear openings. Thus, these portions are not exposed to the UV light. Theresin affinity of these portions is maintained at a low level, providinglow-resin-affinity portions 90 b.

In this modification, the thin film 90 is included in the porous layer20. The portions of the thin film 90 exposed to the UV light areincluded in the surface 23 of the porous layer 20. The portions of thethin film 90 not exposed to the UV light are included in the innersurfaces 21 c of the pores 21 in the porous layer 20.

As illustrated in FIG. 11C, the resin material is applied to the thinfilm 90 to form the transparent substrate 30. At this time, thelow-resin-affinity portions 90 b are present in the inner surfaces 21 cof the pores 21. Thus, the resin material is less likely to enter thepores, thereby maintaining the porosity in the portion of the porouslayer 20 in the vicinity of the surface.

The high-resin-affinity portions 90 a are formed on the surface 23,resulting in high adhesion between the porous layer 20 and thetransparent substrate 30. This prevents accidental detachment of thetransparent substrate 30 from the porous layer 20 in the subsequentsteps in the production process of the electronic device.

While UV light is used for the resin affinity treatment as describedabove, the affinity treatment is not limited thereto. The affinitytreatment may be performed by irradiation with light (visible light) orplasma treatment in place of irradiation with UV light, depending on thetype of the thin film 90.

Another Underlying Knowledge Forming Basis of the Present Disclosure

The present disclosure relates to a method for producing an electronicdevice and a laminated substrate. In particular, the present disclosurerelates to a method for producing an electronic device, in which damageto the electronic device upon separating a supporting substrate isreduced, and relates to a laminated substrate used in the method.

FIG. 28A is a cross-sectional view schematically illustrating a state inwhich an active-matrix organic EL display device serving as anelectronic device not according to an embodiment of the presentdisclosure is used as an example and the electronic device is formed ona supporting substrate. An electron device body 9000 in which anelectronic device 600 (i.e. the organic EL display device) not accordingto an embodiment of the present disclosure is formed on a supportingsubstrate 610 includes the supporting substrate 610 composed of glass, aplastic substrate 630 mainly composed of a resin material, a sealinglayer 640, a thin film transistor (TFT) layer 650, and an organic ELelement layer 660 stacked in that order. The TFT layer 650 and theorganic EL element layer 660 constitute an electronic device elementlayer 670. The plastic substrate 630, the sealing layer 640, and theelectronic device element layer 670 (the TFT layer 650 and the organicEL element layer 660) constitute the electronic device 600.

In the case where an amorphous silicon layer is provided as described inJapanese Patent No. 3809681, laser irradiation generates hydrogen gas asdescribed above. Even if an amorphous silicon layer is not provided,part of the plastic substrate 630 in close contact with the supportingsubstrate 610 is broken by laser irradiation, thereby generating arelatively-high-pressure gas by ablation or pyrolysis, in some cases.The gas generation causes mechanical tensile displacement between aportion where separation proceeds and an adjacent portion that remainsin contact and at the interface between the supporting substrate 610 andthe plastic substrate 630. The plastic substrate 630 has lower stiffnessthan that of the supporting substrate 610. Thus, the plastic substrate630 is deformed so as to be lifted by the pressure of generated gas G asillustrated in FIG. 28B. The deformation of the plastic substrate 630applies stress to the layers arranged on the plastic substrate 630 andthe electronic device element, easily causing damage. In particular, thesealing layer 640 formed of a thin silicon nitride film, the TFT layer650 including the electrode layer formed of a thin metal film, and soforth are susceptible to damage.

In a method for producing an electronic device, the method includingforming an electronic device element on or above a plastic film arrangedon a supporting substrate and then separating the supporting substrate,the inventors have conducted intensive studies in order to suppressdamage to the device at the time of the separation of the supportingsubstrate.

In a method for producing an electronic device according to an aspect ofthe present disclosure, a porous layer is formed between a supportingsubstrate and a resin substrate. At least part of a region of the porouslayer contains a plurality of pores containing a gas in internal spacesthereof. The gas is present in the pores, in other words, the pores haveinternal spaces; hence, in the at least part of the region, the porouslayer has lower stiffness than that of the resin substrate. The porouslayer is easily deformed and broken, compared with the resin substrate.Thus, the at least part of the porous layer is deformed and broken bythe pressure of a gas generated from the resin substrate broken byablation and so forth due to irradiation with laser light, so that thepressure of the gas is relieved, thus reducing stress imposed on theresin substrate. This suppresses damage to the electronic device elementformed on or above the resin substrate.

In a laminated substrate according to another aspect of the presentdisclosure, for the same reason as above, it is possible to reducestress imposed on the resin substrate. In the case where an electronicdevice element and so forth (e.g. the electronic device element and somecomponents thereof) are formed on or above a resin substrate, it ispossible to suppress damage to the electronic device element and soforth.

In a method for producing an electronic device according to an aspect ofthe present disclosure, a supporting substrate is prepared. A porouslayer is formed on or above the supporting substrate, at least part of aregion of the porous layer containing a plurality of pores containing agas in their internal spaces. A resin substrate is formed on or abovethe porous layer. An electronic device element is formed on or above theresin substrate. Irradiation with laser light is performed from thesupporting substrate side to separate the supporting substrate from theresin substrate.

In the production method, the at least part of the region of the porouslayer contains the plurality of pores having internal spaces, so thatthe porous layer has lower stiffness than that of the resin substrate.The energy of the pressure of a gas possibly generated from the resinsubstrate at the time of the laser light irradiation is consumed tobreak the porous layer. This reduces stress on the resin substrate andsuppresses the deformation of the resin substrate, thus suppressingdamage to the electronic device element formed on or above the resinsubstrate.

The pores in a portion of the porous layer adjacent to the resinsubstrate may have a smaller average diameter than that of the pores ina portion of the porous layer adjacent to the supporting substrate.

Since the porous layer has the foregoing structure, when the resinsubstrate is formed on or above the porous layer, a resin material forthe resin substrate is less likely to enter the pores whose innersurfaces are exposed at the main surface of the porous layer adjacent tothe resin substrate. It is thus possible to maintain the internal spacesof the pores present in a surface layer portion on the side of the mainsurface and suppress an increase in the stiffness of the surface layerportion on the side of the main surface of the porous layer. Thisprevents the fact that the pressure of a gas generated at the time ofthe laser light irradiation causes difficulty in breaking the porouslayer. It is thus possible to maintain the effect of reducing stress onthe resin substrate.

Here, the pressure of the gas generated by the laser light irradiationis reduced by breaking the porous layer. In addition, the pressure isreduced by the distribution of the pressure to the gas present in thepores in the porous layer. In particular, when a plurality of porescommunicate with each other, it is possible to obtain a higher effect ofdistributing pressure. Since the porous layer has the foregoingstructure, the internal spaces of the pores present in the surface layerportion on the side of the main surface of the porous layer aremaintained, thus maintaining the gas-pressure distributing effect.

The porous layer may include a first porous sublayer portion on thesupporting substrate; and a second porous sublayer on the first poroussublayer. The pores in the second porous sublayer may have a smalleraverage diameter than that of the pores in the first porous sublayer.

In this case, a resin material for the resin substrate is less likely toenter the pores in the second porous sublayer located on the side onwhich the resin substrate is arranged. Thus, the internal spaces of thepores are maintained, thereby maintaining the effect of reducing stresson the resin substrate. Moreover, the effect of distributing thepressure of a gas generated at the time of laser light irradiation ismaintained. The first porous sublayer having the pores with an averagediameter larger than that of the second porous sublayer is arranged on aside of the second porous sublayer adjacent to the supporting substrate.This reduces the stiffness of the entire porous layer to suppress thedeformation of the resin substrate.

The second porous sublayer may be formed by a dry process or thermalevaporation.

In the case where the second porous sublayer is formed by a wet process,water and a solvent is left. This causes the generation of a gas at thetime of heating and laser irradiation in the subsequent productionprocess. Since the second porous sublayer is formed by a dry process orthermal evaporation, water and a solvent is not left, therebysuppressing the generation of a gas.

The first porous sublayer may be formed by the application of a firstresin material. The second porous sublayer may be formed by theapplication of a second resin material. The second resin material mayhave a higher viscosity than that of the first resin material.

In this case, when the second porous sublayer is formed on the firstporous sublayer, the second resin material is less likely to enter thepores exposed at a main surface of the first porous sublayer on the sideon which the second porous sublayer is formed, thus maintaining theinternal spaces of the pores in the first porous sublayer. As a result,the entire porous layer has lower stiffness than that of the resinsubstrate.

In a state after the formation of the porous layer and before theformation of the resin substrate, some inner surfaces of the pluralityof pores may be exposed at a surface serving as a main surface of theporous layer on the side on which the resin substrate is to be formed.Moreover, after the formation of the porous layer and before theformation of the resin substrate, the porous layer may be subjected toaffinity treatment such that the affinity of the surface of the porouslayer for a resin material used to form the resin substrate is higherthan the affinity of a portion of the porous layer other than thesurface.

In this case, when the resin substrate is formed by the application ofthe resin material on the porous layer, the resin material is lesslikely to enter the inside the pores exposed at the main surface of theporous layer on the side on which the resin substrate is formed. Thus,the internal spaces of the pores in the porous layer are maintained,thereby maintaining the effect of reducing stress on the resinsubstrate. Moreover, the effect of distributing the pressure of a gasgenerated at the time of laser light irradiation is maintained.

In the affinity treatment, after a thin film of a material is formed onthe surface and the inner surfaces of the porous layer, the UV lightirradiation or the plasma treatment may be performed from the side onwhich the resin substrate is to be formed. The material of the thin filmhave a lower affinity for the resin material than a material used toform the porous layer, and have properties in which the affinity afterUV light irradiation or plasma treatment is higher than the affinitybefore the UV light irradiation or the plasma treatment.

The thin film may be formed by applying a solution containing a materialto the surface and the exposed inner surfaces of the porous layer andperforming drying. The material have a lower affinity for the resinmaterial than the material used to form the porous layer, and haveproperties in which the affinity after UV light irradiation or plasmatreatment is higher than the affinity before the UV light irradiation orthe plasma treatment.

In this case, the affinity treatment is easily performed.

The pores in the portion of the porous layer adjacent to the resinsubstrate may have an average diameter of 1 μm or less.

In this case, when the resin substrate is formed on the porous layer,the resin material is less likely to enter the pores exposed at the mainsurface of the porous layer on the side on which the resin substrate isformed. Thus, the internal spaces of the pores in the portion of theporous layer adjacent to the resin substrate are maintained, therebymaintaining the effect of reducing stress on the resin substrate.Moreover, the effect of distributing the pressure of a gas generated atthe time of laser light irradiation is maintained.

The pores in the second porous sublayer may have an average diameter of1 μm or less.

In this case, when the resin substrate is formed on the second poroussublayer, the resin material is less likely to enter the pores exposedat the main surface of the second porous sublayer on the side on whichthe resin substrate is formed. Thus, the internal spaces of the pores inthe portion of the second porous sublayer adjacent to the resinsubstrate are maintained, thereby maintaining the effect of reducingstress on the resin substrate. Moreover, the effect of distributing thepressure of a gas generated at the time of laser light irradiation ismaintained.

The porous layer may include a coating thin layer portion free from thepores, the coating thin layer portion being arranged on a surfaceserving as a main surface of the porous layer on the side on which theresin substrate is formed. The coating thin layer portion may becomposed of a material that is the same as that constituting a portionof the porous layer other than the coating thin layer portion.

In this case, when the resin substrate is formed on the porous layer,the resin material is blocked by the coating thin layer portion and doesnot enter the pores in the porous layer. Thus, the internal spaces ofthe pores in the porous layer are maintained, thereby maintaining theeffect of reducing stress on the resin substrate. Moreover, the effectof distributing the pressure of a gas generated at the time of laserlight irradiation is maintained. Furthermore, the coating thin layerportion is composed of a material that is the same as that constitutingthe portion of the porous layer other than the coating thin layerportion. Thus, increases in the number of steps and the types ofmaterials are suppressed, leading to the suppression of an increase inproduction cost.

A laminated substrate according to another embodiment of the presentdisclosure includes a supporting substrate, a porous layer arranged onor above the supporting substrate, at least part of a region of theporous layer containing a plurality of pores containing a gas ininternal spaces thereof, and a resin substrate arranged on or above theporous layer.

In the structure of the laminated substrate according to the anotheraspect of the present disclosure, the at least part of the region of theporous layer contains the plurality of pores having internal spaces, sothat the porous layer has lower stiffness than that of the resinsubstrate. In the case where after an electronic device element and itscomponent are partially formed, the supporting substrate is separated byirradiation with laser light from the supporting substrate side, theenergy of the pressure of a gas possibly generated from the resinsubstrate at the time of the laser light irradiation is consumed tobreak the porous layer. This reduces stress on the resin substrate andsuppresses the deformation of the resin substrate, thus suppressingdamage to the electronic device element and so forth formed above theresin substrate.

The pores in a portion of the porous layer adjacent to the resinsubstrate may have a smaller average diameter than that of the pores ina portion of the porous layer adjacent to the supporting substrate.

Thus, when the resin substrate is formed on or above the porous layer, aresin material for the resin substrate is less likely to enter the poreswhose inner surfaces are exposed at the main surface of the porous layeradjacent to the resin substrate. It is thus possible to maintain theinternal spaces of the pores present in a surface layer portion on theside of the main surface and suppress an increase in the stiffness ofthe surface layer portion on the side of the main surface of the porouslayer. This prevents the fact that the pressure of a gas generated atthe time of the laser light irradiation causes difficulty in breakingthe porous layer. It is thus possible to maintain the effect of reducingstress on the resin substrate.

The internal spaces of the pores present in the surface layer portion ofthe porous layer are maintained, so that the pressure of the gasgenerated by the laser irradiation is distributed to the gas present inthe internal spaces of the pores. Stress due to the pressure of the gason the resin substrate is thus reduced.

Embodiments and modifications thereof of the present disclosure will bespecifically illustrated below. The structure, the effects, and theadvantages will be described.

The embodiments and the modifications described below are merelyexamples to clearly illustrate the structures according to an aspect ofthe present disclosure and the effects and advantages thereof. Thepresent disclosure is in no way limited to the following embodiments andmodifications, except for its inessential features.

Second Embodiment

1. Structure of Electronic Device

The structure of an electronic device according to a second embodimentof the present disclosure will be described below with reference toFIGS. 14A, 14B, 15, and 16A to 16D by taking, as an example, anactive-matrix organic EL display device for which the structure is used.

FIG. 14A is a partial cross-sectional view schematically illustratingthe structure of an electron device body 4000 in which an electronicdevice 400 according to this embodiment is arranged on a supportingsubstrate 310. In this embodiment, the electronic device 400 is anactive-matrix organic EL display device. FIG. 14B is a partialcross-sectional view schematically illustrating a state in which theelectron device body 4000 is irradiated with laser light from thesupporting substrate 310 side.

As illustrated in FIG. 14A, the electron device body 4000 includes thesupporting substrate 310, a porous layer 320, a plastic substrate (orresin substrate) 330, a sealing layer 340, a TFT layer 350, and anorganic EL element layer 360 stacked in that order. The TFT layer 350and the organic EL element layer 360 constitute an electronic deviceelement layer (electronic device element) 370. The plastic substrate330, the sealing layer 340, the TFT layer 350, and the organic ELelement layer 360 constitute the electronic device 400 according to thisembodiment. The supporting substrate 310, the porous layer 320, and theplastic substrate 330 constitute a laminated substrate 301 according tothis embodiment.

Supporting Substrate

Examples of a material for the supporting substrate 310 include, but arenot particularly limited to, glass materials, such as alkali-free glass(borosilicate glass), alkali glass, soda glass, non-fluorescent glass,phosphate-based glass, borate glass, and silica; and insulatingmaterials, such as alumina.

A surface of the supporting substrate 310 (i.e. a main surface of thesupporting substrate 310 on the side on which the electronic device 400is to be formed) desirably has a high degree of flatness because athin-film device element, such as a display device element, is formedafter the temporal fixation of the plastic substrate 330. Specifically,the surface has a maximum level difference of 10 μm or less anddesirably 1 μm or less.

The surface of the supporting substrate 310 is desirably in a cleanstate in order to achieve good adhesion to a layer to be formed thereon.As a method for cleaning the surface, for example, UV light irradiation,ozone treatment, plasma treatment, or hydrofluoric acid treatment may beemployed. A single layer configured to improve adhesion to a layer to beformed thereon may be formed on a surface of the supporting substrate310. As the layer configured to improve adhesion, for example, a siliconoxide film may be used.

Porous Layer

As illustrated in FIG. 15, the porous layer 320 has many pores therein.FIG. 15 is a scanning electron photomicrograph of a cross section of aportion in the vicinity of the interface between the porous layer 320and the plastic substrate 330.

The term “pores” indicates that not all of the internal spaces arefilled with a liquid or a solid and that a gas, for example, air or avaporized solvent, is present. A liquid, for example, water or asolvent, or solid foreign matter, such as dust, may be present in theinternal spaces in addition to the gas. However, even in this case, 50%or more of the volume of each of the internal spaces is desirably filledwith a gas.

The porosity of the porous layer 320 is higher than at least theporosity of the plastic substrate 330. The stiffness of at least part ofthe porous layer 320 is lower than the stiffness of the plasticsubstrate 330.

Here, the term “pores” are not limited to cell-like pores havingcompletely closed internal spaces and is used as a concept includingpores in which part of a cell-defining wall is absent, pores in which adefective portion of a wall is exposed at the outside, and pores inwhich the internal spaces of a plurality of cells communicate with eachother.

Furthermore, the term “pores” used here indicates pores each having adiameter of, for example, 10 nm or more and 10 μm or less, and desirably100 nm or more and 5 μm or less. In the case where a plurality of porescommunicate with each other, each of the pores may have a diameterwithin the above range.

Here, the diameter of each of the pores indicates the length of theinternal space of each pore in the direction to which a layer extends(i.e. direction perpendicular to the thickness direction of the layer).

Specifically, the porous layer 320 desirably has a porosity of, forexample, 10% or more and 90% or less.

More desirably, the porous layer 320 may have a porosity of 50% or moreand 90% or less. A porosity of 50% or more results in an increase in theproportion of the porous layer broken upon separating the supportingsubstrate with a laser, thereby resulting in a reduction in pressureapplied to the plastic substrate. At a porosity of 90% or less, theporous layer 320 ensures mechanical strength to a certain degree. Forexample, it is possible to suppress breakage due to mechanical stresscaused by, for example, a reduction or an increase in pressure at thetime of vacuum deposition in a production process. Specifically, thebreakage due to mechanical stress indicates the delamination of a filmand so forth. At an excessively high porosity, when the plasticsubstrate 330 is formed with a resin material (for example, polyimide),the resin material enters the pores, increasing the strength of theporous layer 320. Thus, the porous layer 320 desirably has a porosity ofabout 90% or less.

As a method for measuring the porosity of the porous layer 320, there isa method as described below. For example, a cross section of the porouslayer 320 is formed by mechanical cutting or focused ion beammicromachining. The cross section is observed with a scanning electronmicroscope. The ratio of pores at the cross section to the division walldefining the pores is calculated. It is easily assumed that a comparableratio is obtained in another cross section. Thus, the ratio isdetermined as a volume ratio and may be defined as the porosity.Furthermore, the measurement is performed at a plurality of points inthe cross section. It is possible to increase the accuracy by averagingthe resulting values of the porosity.

As the material for the porous layer 320, an organic material may beused.

Examples of a method for forming the porous layer 320 include, but arenot particularly limited to, a wet formation method and a dry formationmethod. A temperature during a step of forming the porous layer 320 or aheating temperature after the formation of the porous layer 320 isdesirably higher than a temperature in a step of forming each layerformed thereon. The reason for this is that when the steps of formingthe upper layers are performed at a higher temperature than theformation temperature of the porous layer 320, the porous layer 320 islikely to change, which is not desirable. For example, water, a solvent,and a gas adsorbed in the pores or on a solid portion of the porouslayer 320 may be desorbed at the time of the formation steps of theupper layers, causing a failure, such as separation from the upperlayer.

The thickness of the porous layer 320 is desirably, but not particularlylimited to, about 1 μm to about 1000 μm.

In this embodiment, as illustrated in FIG. 15, the porous layer 320includes a coating thin layer portion 322 on the surface of the porouslayer 320 adjacent to the plastic substrate 330, the coating thin layerportion 322 having a thickness of about 1 μm and being free from a pore.Since the coating thin layer portion 322 is arranged, when a resinmaterial used to form the plastic substrate 330 is applied to the porouslayer 320, the resin material does not enter the pores, so that theinternal spaces of the pores are not filled with the resin material.This satisfactorily maintains the gas-pressure-relief effect of theporous layer 320.

The term “resin material” used here includes resin polymers andsolvents. The resin polymers and the solvents each may be used incombination as a mixture of two or more types thereof.

In the formation process of the porous layer 320, when a resin materialused to form the porous layer 320 is heated, a solvent in the resinmaterial seemingly bubbles to form pores. At this time, bubbles near asurface can be relatively easily moved from the surface to the air. Thebubbles seemingly disappear in near the surface as time passes, therebyforming the coating thin layer portion 322.

Plastic Substrate

Examples of a material for the plastic substrate 330 include, but arenot particularly limited to, polyethylene, polypropylene, polyvinylene,polyvinylidene chloride, polyethylene terephthalate, polyethylenenaphthalate, polycarbonate, polyethylene sulfonic acid, silicone,acrylic resins, epoxy resins, phenolic resins, polyamide, polyimide, andaramid resins. These materials may be used in combination as a mixtureof two or more thereof. These materials may be chemically modified. Twoor more of these materials may be combined to form a laminated filmhaving a multilayer structure.

The plastic substrate 330 is required to have the characteristics inwhich the plastic substrate 330 is not easily cracked or broken whencurved. If the plastic substrate 330 does not have the characteristics,it is impossible to provide a display device with high flexibility.

The thickness of the plastic substrate 330 is desirably in the range of1 μm to 1000 μm. At a thickness smaller than the range, mechanicalstrength is not ensured. At a thickness larger than the range, thesubstrate is difficult to bend, thus failing to provide a display devicewith high flexibility.

Regarding a method for forming the plastic substrate 330, the plasticsubstrate 330 may be formed by the application of a liquid resinmaterial. A film-shaped material may be press-bonded, without anylimitation. When the film-shaped material is press-bonded, an adhesivelayer may be formed between the film and the porous layer. The adhesivelayer is not particularly limited as long as a desired adhesive force isprovided. Examples of the adhesive layer include silicone-based adhesivelayers and acrylic-based adhesive layers. The plastic substrate 330 maybe the transparent substrate 30 described above.

Sealing Layer

The sealing layer 340 may be formed of, for example, a silicon nitridefilm.

TFT Layer

The TFT layer 350 includes a TFT configured to drive an organic ELelement. The TFT layer 350 includes an electrode layer 351 formed of agate electrode included in the TFT, and a TFT main body layer 352constituting a portion of the TFT except the gate electrode.

The electrode layer 351 is formed by depositing a metal material by avacuum evaporation method or a sputtering method and selectivelyremoving the resulting metal material film by, for example, etching.Examples of a material for the electrode layer 351 include silver,aluminum, alloys of silver, palladium, and copper, and alloys of silver,rubidium, and gold.

The TFT main body layer 352 includes, for example, a gate-insulatingfilm, source-drain electrodes, a bank, a semiconductor layer, and apassivation film. Examples of the TFT that may be used include a TFTwhose channel material is silicon, a TFT whose channel material is anoxide semiconductor, such as an indium-gallium-zinc oxide, and a TFTwhose channel material is an organic semiconductor, such as pentacene.

Organic EL Element Layer

The organic EL element layer 360 includes a cathode, an anode, and alight-emitting layer arranged between the cathode and the anode. Theorganic EL element layer 360 may further include an electron injectionlayer, an electron transport layer, a hole injection layer, a holetransport layer, a partition layer, a sealing layer, and so forth. Theorganic EL element layer 360 may still further include a color filterand a protective filter.

The TFT layer 350 and the organic EL element layer 360 constitute theelectronic device element layer 370.

In this embodiment, the TFT layer 350 has a multilayer structureincluding the electrode layer 351 and the TFT main body layer 352.However, the TFT layer 350 is not limited to the structure. For example,in the case where the electronic device 400 is a passive-matrix organicEL display device, a wiring layer corresponds to the TFT layer 350.

In the case where the electronic device 400 is a liquid crystal displaydevice, LCD elements are arranged in the display device element layer370. In the case where the electronic device 400 is a photosensor, aphotoelectric conversion element is arranged in the electronic deviceelement layer 370.

2. Separation Between the Electronic Device and the Supporting Substrate

To separate the electronic device 400 from the supporting substrate 310,irradiation with laser light is performed from the supporting substrate310 side. Thereby, part of the porous layer 320 is broken at theinterface between the supporting substrate 310 and the porous layer 320,at the inside of the porous layer 320, or at the interface between theporous layer 320 and the plastic substrate 330, thus separating theelectronic device 400 from the supporting substrate 310.

In the case of the electron device body 9000 which is not according tothis embodiment and which is illustrated in FIG. 28A, a plasticsubstrate 630 is arranged on the supporting substrate 610. Themechanical stress due to laser irradiation is not relieved, so that theplastic substrate 630 is markedly deformed as illustrated in FIG. 28B.Specifically, the deformation of the plastic substrate 630 iselongation. The rate of change is expressed as [(d+Δd)/d]⁻¹, where drepresents an elongation state before the laser irradiation, and d+Δdrepresents an elongation state after the laser irradiation. For example,in the case of a plastic substrate including an inorganic siliconnitride film generally used as a sealing film, the marginal rate ofchange, at which a barrier is broken, is in the range of about 0.5% toabout 1.0%. This reveals that even a minute change causes damage to theupper layers. The cause of the deformation is as follows: When theplastic substrate 630 absorbs the energy of the laser light to causeablation, a high-pressure gas is generated. However, the pressure cannotescape through the supporting substrate 610; hence, the energy isconsumed to deform the plastic substrate 630.

In contrast, in the method for producing an electronic device accordingto this embodiment, the porous layer 320 is formed between thesupporting substrate 310 and the plastic substrate 330.

The porous layer 320 has a shape containing the pores therein and haslower stiffness than that of the supporting substrate 310 and theplastic substrate 330. Thus, as illustrated in FIG. 14B, the energy ofhigh-pressure gas G generated by ablation or pyrolysis due to laserirradiation is consumed by the break and deformation of the porous layer320. Moreover, the pressure is relieved by the internal spaces of theporous layer 320. Thereby, the deformation of the plastic substrate 330is suppressed. Furthermore, the deformation of the layers arranged abovethe plastic substrate 330 is also suppressed.

In the case where a plurality of pores communicate with each other, agas generated from the resin substrate is dispersed in the plural porescommunicating with each other to relieve the pressure. This also reducesstress on the resin substrate.

In addition, the break of the mechanically fragile porous layer 320causes a loss of the bonding force between atoms or molecules in theporous layer 320, or the bonding force between the plastic substrate 330and the porous layer 320, thereby stably and easily separating theplastic substrate 330 from the supporting substrate 310.

In the case where the porous layer 320 is arranged, it is possible tosuppress the deformation of the plastic substrate 330 even when theintensity of laser light is increased in order to improve the efficiencyof a separation process. The porous layer 320 is susceptible tomechanical breakage. Thus, the area ratio that maintains adhesion islow, so that the separation process is stably performed.

As has been described above, the use of the structure according to theembodiment of an aspect of the present disclosure suppresses (orreduces) damage to the electronic device at the time of the separationof the supporting substrate. Furthermore, it is possible to easily andstably perform the separation of the supporting substrate 310.

3. Method for Producing Electronic Device

A method for producing an electronic device according to an embodimentof an aspect of the present disclosure will be described below withreference to FIGS. 16A to 16D, 17A to 17C, 18A, 18B, and 19. FIGS. 16Ato 16D, 17A to 17C, 18A, and 18B are partial cross-sectional viewsschematically illustrating some steps in a procedure for producing theelectronic device 400 according to the embodiment. FIG. 19 is aschematic flow chart of the procedure for producing the electronicdevice 400 according to the embodiment.

As illustrated in FIG. 16A, the supporting substrate 310 is prepared(step S11 in FIG. 19). The supporting substrate 310 is subjected toexcimer UV (wavelength: 172 nm) treatment to clean the surface.

As illustrated in FIG. 16B, the porous layer 320 is formed on thesupporting substrate 310 (step S12 in FIG. 19).

As illustrated in FIG. 16C, the plastic substrate 330 serving as asubstrate for a flexible display is formed on the porous layer 320 (stepS13 in FIG. 19). Thereby, the laminated substrate 301 is provided.

As illustrated in FIG. 16D, the sealing layer 340 is formed on theplastic substrate 330 (step S14 in FIG. 19).

As illustrated in FIG. 17A, a thin metal film is formed on the sealinglayer 340 and then is subjected to etching treatment, thereby formingthe electrode layer 351 (step S15 in FIG. 19).

As illustrated in FIG. 17B, the TFT main body layer 352 is formed on theelectrode layer 351, thereby completing the TFT layer 350 (step S16 inFIG. 19). In the case where a passive-matrix display is formed, the TFTlayer need not be formed. A wiring layer alone will suffice.

As illustrated in FIG. 17C, the organic EL element layer 360 is formedon the TFT layer 350 (step S17 in FIG. 19). Thereby, the electron devicebody 4000 is provided.

As illustrated in FIG. 18A, the electron device body 4000 is irradiatedwith laser light from the supporting substrate 310 side (step S18 inFIG. 19).

The supporting substrate 310 and the porous layer 320 are separated fromthe plastic substrate 330 by the laser irradiation, thereby providingthe electronic device 400 (step S19 in FIG. 19).

After the separation of the supporting substrate 310 and the porouslayer 320, part of the porous layer 320 may be attached to the plasticsubstrate 330.

4. Damage-Suppressing Effect

A verification test was performed to prove the effect of suppressingdamage to the electronic device in a method for producing an electronicdevice according to an embodiment of an aspect of the presentdisclosure. The verification test was performed using two types of testpieces TP1 and TP2, which had the porous layers 320 with differentthicknesses, and, as a comparative example, test piece TP3, which wasfree from the porous layer 320. In each of test pieces TP1, TP2, andTP3, the TFT main body layer 352 and the organic EL element layer 360were not formed. The verification test was performed by subjecting testpieces TP1, TP2, and TP3 to laser irradiation and observing andmeasuring the surface state of the electrode layer 351.

Test Piece TP1

A specific method for producing test piece TP1 and production conditionswill be described below.

The supporting substrate 310 was prepared (FIG. 16A, step S11 in FIG.19). As the supporting substrate 310, EAzLE 2000, manufactured byCorning Incorporated, was used. A surface of the supporting substrate310 was subjected to excimer UV (wavelength: 172 nm) treatment to cleanthe surface.

A polyimide was applied to the supporting substrate 310 by a spincoating method. The applied polyimide was heated at a heatingtemperature of 400° C. for 8 hours, thereby forming a 18-μm-thick porouspolyimide layer serving as the porous layer 320 (FIG. 16B, step S12 inFIG. 19). Regarding the polyimide used as a material for the porouslayer 320, specifically, U Imide Varnish Type BP manufactured by UnitikaLimited was used.

A polyimide layer having a thickness of 30 μm was formed by a spincoating method on the porous layer 320, thereby forming the plasticsubstrate 330 serving as a substrate for a flexible display (FIG. 16C,step S13 in FIG. 19). Regarding the polyimide used as a material for theplastic substrate 330, specifically, U-Varnish manufactured by UbeIndustries, Ltd. was used.

A 1-μm-thick silicon nitride film serving as the sealing layer 340 wasformed on the plastic substrate 330 by capacitively coupledplasma-enhanced CVD at 300° C. (FIG. 16D, step S14 in FIG. 19).

A 100-nm-thick layer composed of an alloy of molybdenum and tungsten wasformed on the sealing layer 340 by a sputtering method. The layer waspatterned by a photolithography method with a resist and then subjectedto etching treatment with a liquid mixture of phosphoric acid, nitricacid, and acetic acid, thereby forming the electrode layer 351 (FIG.17A, step S15 in FIG. 19). In this way, test piece TP1 was produced. Aschematic cross-sectional view of test piece TP1 is illustrated in FIG.20A.

Test Piece TP2

Test piece TP2 was produced in the same procedure as test piece TP1,except that a 117-μm-thick porous polyimide serving as the porous layer320 was formed at a reduced spin-coating speed. A schematiccross-sectional view of test piece TP2 is illustrated in FIG. 20B.

Test Piece TP3

Test piece TP3, as a comparative example, was produced in the sameprocedure as test piece TP1, except that the porous layer 320 was notformed. A schematic cross-sectional view of test piece TP3 isillustrated in FIG. 20C.

At least four specimens for each of test pieces TP1, TP2, and TP3 wasprepared. Each of test pieces TP1, TP2, and TP3 was irradiated withlaser light at four different laser irradiation power densities toseparate a film 302 including the plastic substrate 330, the sealinglayer 340, and the electrode layer 351 from the supporting substrate 310(and the porous layer 320). Three evaluations described below were madefor each test piece. The laser irradiation was performed by irradiationwith excimer laser light having a wavelength of 305 nm, a pulse widthper pulse of 20 ns, and an irradiation area of 20.0 mm×1.0 mm from thesupporting substrate 310 while the excimer laser light is swept.

(1) Whether the plastic substrate 330 could be separated from thesupporting substrate 310 was evaluated. When the separation could beperformed with bare hands with little resistance, the specimen was ratedas separable. In the case where the separation with bare hands isdifficult to perform because of high adhesion between the film 302 andthe supporting substrate 310, a technique for the separation by theapplication of a force with a roller or the like is conceivable.However, when a force is applied, the plastic substrate 330 is deformedto cause damage to the sealing layer 340 and the electrode layer 351arranged as upper layers, which is undesirable.

(2) The laser irradiation was repeated until the separation could beperformed with bare hands with little resistance at each laserirradiation power density. The number of repetitions of the irradiationwas evaluated as an index of the process speed.

(3) After the separation of the supporting substrate 310, a surface ofthe electrode layer 351 was observed with a microscope to inspect theelectrode layer 351 for defects, such as cracking.

FIG. 21 illustrates the results of the three evaluations.

In test piece TP3, when the laser irradiation energy density was 140mJ/cm², the laser power was excessively low and did not reach athreshold of energy density required for the ablation of the polyimide.Thus, increasing the number of repetitions of the irradiation failed toperform the separation. When the laser irradiation energy density was180 mJ/cm² or more, the following results were observed: a high-pressuregas (decomposition product of the polyimide) was generated by ablationdue to the laser irradiation to deform the plastic substrate 330,causing damage to the electrode layer 351 composed of themolybdenum-tungsten alloy arranged on the plastic substrate 330.

FIG. 22A is a photomicrograph of a surface of the electrode layer 351 oftest piece TP3 after the laser irradiation. FIG. 22B is a schematic viewof the state of the surface of the electrode layer 351 of thephotomicrograph in FIG. 22A, for simplicity's sake. As illustrated inFIGS. 22A and 22B, streaky portions 351 a that look likeleaf-vein-shaped cracks and point-defect portions 351 b that look likethrough-holes or recessed portions were observed on the surface of theelectrode layer 351 of test piece TP3 after the laser irradiation.

The sealing layer 340 arranged below the electrode layer 351 isseemingly deformed with the deformation of the plastic substrate 330,thereby breaking the electrode layer 351 arranged on the sealing layer340. In test piece TP3 that did not include the porous layer 320, whenthe laser irradiation energy density was 160 mJ/cm², conditions underwhich the separation was made and electrode cracking did not occur wereobtained. In the conditions, however, it is necessary to perform 20 ormore laser irradiation operations in order to stably perform theseparation with bare hands. For example, in the case of a process with afourth-generation large-area glass substrate, it takes a long time of 5or more hours to subject the entire surface to laser treatment, which isimpractical in terms of production efficiency.

Here, as illustrated in FIG. 15, in the porous layer 320 according tothe embodiment, the diameters of pores 321 a in a portion near theplastic substrate 330 are generally smaller than those of pores 321 b ina portion further away from the plastic substrate 330 (portion adjacentto the supporting substrate 310). In other words, the average diameterof the pores 321 a is smaller than the average diameter of the pores 321b. The term “average diameter” may be represented by an average diameterobtained in an area of 10×10 μm². For example, the average diameter maybe represented by an average diameter obtained by the observation of twoor three points in a cross section of the porous layer 320 with afocused ion beam (FIB) scanning electron microscope (SEM).

The results of the laser separation on test pieces TP1 and TP2illustrated in FIG. 21 reveal two features, compared with test piece TP3not including the porous layer 320. First, no cracks were observed inthe electrode layer 351 at the high-energy densities (180 and 200mJ/cm²). The reason for this is that the advantageous effects of thepresent disclosure were provided, in other words, the energy of a gasgenerated by ablation or pyrolysis due to laser irradiation was consumedto break the porous layer 320 without being used for the deformation ofa portion on the plastic substrate 330 side. Furthermore, a lower regionof the porous layer 320 (i.e. region adjacent to the supportingsubstrate 310) has high porosity because the pores in the region havelarge diameters; hence, stress due to the gas generated from the plasticsubstrate 330 is more likely to be absorbed in the porous layer 320.

FIGS. 23A, 23B, and 23C are photomicrographs of the surfaces of theelectrode layers 351 of test pieces TP1, TP2, and TP3 after laserirradiation at an energy density of 180 mJ/cm². To further clarify theinfluence of the laser irradiation, these photomicrographs were takenafter the laser irradiation had been intentionally performed not on theentire surface but on linear regions. In FIGS. 23A, 23B, and 23C, rangesindicated by arrows show ranges that have been irradiated with laserlight.

FIG. 24 illustrates the results of measurement of the amounts ofdisplacement in the thickness direction of the surfaces of the electrodelayers 351 of test pieces TP1, TP2, and TP3 illustrated in FIGS. 23A,23B, and 23C, the measurement being performed with a stylus profilometerafter the laser irradiation. In FIG. 24, regions indicated by arrowscorrespond to regions that have been irradiated with laser light.

As illustrated in FIGS. 23A, 23B, 23C, and 24, in test piece TP3, theseparation of the electrode layer 351 was clearly observed. It wasconfirmed that the plastic substrate 330 was lifted by a gas generatedby an ablation phenomenon due to the laser irradiation to cause asignificant deformation of the electrode layer 351. In each of testpieces TP1 and TP2, the amount of displacement of the electrode layer351 was small, compared with test pieces TP3. In test piece TP2, theamount of displacement of the electrode layer 351 was smaller than thatof test piece TP1. As illustrated in FIG. 24, in test piece TP3, theamount of displacement of the electrode layer 351 was about 4 μm. Incontrast, in test piece TP1, the amount of displacement of the electrodelayer 351 was about 1.5 μm or less. In test piece TP2, the amount ofdisplacement of the electrode layer 351 was about 1 μm or less.

Second, when a comparison is made at an energy density of 160 mJ/cm²,for each of test pieces TP1 and TP2, the number of repetitions of laserirradiation until the separation can be performed is very small,compared with test piece TP3. A possible reason for this is as follows:The porous layer 320 has high porosity and thus a small area thatmaintains adhesion, thereby facilitating separation even by a singlelaser irradiation.

Owing to these two effects, the irradiation conditions at a high energydensity can be used, thus reducing the number of repetitions of laserirradiation. Even when the entire surface of a large-sized substrate isprocessed, the time required for the separation treatment of thesupporting substrate can be reduced, which is particularly advantageousfor production.

Specifically, it is desirable that the average diameter of the pores inthe porous layer 320 adjacent to the plastic substrate 330 be, forexample, 10 nm or more and 1 μm or less. It is desirable that theaverage diameter of the pores in the porous layer 320 adjacent to thesupporting substrate 310 be, for example, 100 nm or more and 10 μm orless.

Modifications

While the present disclosure has been described on the basis of theembodiment, the present disclosure is not limited to the foregoingembodiment. The following modifications may be performed.

First Modification

In the foregoing embodiment, the porous layer 320 includes the coatingthin layer portion 322. However, the porous layer 320 is not limitedthereto. The porous layer 320 may have a structure free from the coatingthin layer portion 322.

In this case, the average diameter of the pores in a portion of theporous layer 320 adjacent to the plastic substrate 330 is desirablysmaller than the average diameter of the pores in a portion of theporous layer 320 adjacent to the supporting substrate. In the case of asmaller average diameter of the portion of the porous layer 320 adjacentto the plastic substrate 330, a resin material that has been appliedupon forming the plastic substrate 330 is less likely to enter thepores. Thus, the porosity of the porous layer 320 is maintained, therebymaintaining the effect of relieving the pressure of a gas generated byablation.

The porous layer 320 is formed by applying a resin material and thenheating the applied resin material. In general, bubbles of a solventdisappear more easily at a position closer to a surface. Thus, the porescloser to the surface have a smaller average diameter. The heatingtemperature, the heating time, and the type and amount of the solvent inthe resin material at the time of the formation of the porous layer 320may be adjusted in such a manner that the coating thin layer portion 322is not formed.

Second Modification

In the case where the plastic substrate 330 is bonded to the porouslayer 320, as illustrated in FIG. 25A which illustrates an electrondevice body 5000 according to a second modification, an adhesive layer380 may be provided between the porous layer 320 and the plasticsubstrate 330. The adhesive layer 380 is typically formed byapplication. Thus, when the pores in a surface portion of the porouslayer 320 on the side on which the plastic substrate 330 is formed havea smaller average diameter, a material constituting the adhesive layeris less likely to penetrate into the pores. Also in the case of thebonding, when the pores in the surface portion of the porous layer 320on the side on which the plastic substrate 330 is formed have a smalleraverage diameter, a larger area of a surface of the porous layer 320 inclose contact with the plastic substrate 330 is provided, compared withthe case of a large average diameter, thereby increasing the adhesion tothe plastic substrate 330. This prevents accidental detachment of theplastic substrate 330 from the porous layer 320 in the course of theproduction process of the electronic device.

The supporting substrate 310, the porous layer 320, the adhesive layer380, and the plastic substrate 330 constitute a laminated substrate 5001according to the second modification.

Third Embodiment

The porous layer may include two or more sublayers. FIG. 25B is apartial cross-sectional view of an electron device body 3000 accordingto a third modification. As illustrated in FIG. 25B, in the electrondevice body 3000, a porous layer 3020 includes a first porous sublayer3020 a on the supporting substrate 310, and a second porous sublayer3020 b on the first porous sublayer 3020 a. In this case, the averagediameter of pores in the second porous sublayer 3020 b is desirablysmaller than the average diameter of pores in the first porous sublayer3020 a. In the case where the plastic substrate 330 is formed byapplication on the second porous sublayer 3020 b, when the pores in thesecond porous sublayer 3020 b have a smaller average diameter, a resinmaterial is less likely to enter the pores, thereby maintaining theporosity of the second porous sublayer 3020 b. This relieves thepressure of a gas generated by ablation due to laser irradiation tosuppress the deformation of the plastic substrate, thereby suppressingdamage to the device.

Even in the case where the porous layer 320 is formed of a single layeror multiple sublayers, desirably, the pores in a portion having athickness of at least ½ or more of the thickness of the porous layer 320are not filled with the resin material for the plastic substrate 330.

Furthermore, an additional layer(s) may be arranged between thesupporting substrate 310 and the first porous sublayer 3020 a and/orbetween the first porous sublayer 3020 a and the second porous sublayer3020 b.

The supporting substrate 310, the porous layer 3020, and the plasticsubstrate 330 constitute a laminated substrate 3001 according to thethird modification.

Fourth Modification

In the case where the porous layer 3020 includes the first poroussublayer 3020 a and the second porous sublayer 3020 b like thirdmodification, the second porous sublayer 3020 b may be formed by any oneof dry processes selected from a chemical vapor deposition method, asputtering method, and an evaporation method. When the second poroussublayer 3020 b is formed by a wet process, water and a solvent are leftin the pores and a solid portion of the second porous sublayer 3020 b.This causes the generation of a gas by heating and laser irradiation inthe subsequent production process. In the case where the second poroussublayer 3020 b is formed by a dry process or thermal evaporation, waterand a solvent are not left, thereby inhibiting the generation of a gas.

Fifth Modification

A second resin material used to form the second porous sublayer 3020 bdesirably has a higher viscosity than that of a first resin materialused to form the first porous sublayer 3020 a. In this case, the secondresin material used to form the second porous sublayer 3020 b is lesslikely to enter the pores in the first porous sublayer 3020 a, therebymaintaining the porosity of the first porous sublayer 3020 a.

Sixth Modification

Affinity treatment may be performed after a step of forming the porouslayer 320 and before a step of forming the plastic substrate 330. Theaffinity treatment may be performed such that the affinity of a surface323 of the porous layer 320 (i.e. a main surface of the porous layer 320on the side on which the plastic substrate 330 is to be formed) for theresin material used to form the plastic substrate 330 (hereinafter,referred to simply as “resin affinity”) is higher than the resinaffinity of inner surfaces 321 c of pores 321 exposed at the surface323.

A method of the affinity treatment will be described below withreference to FIGS. 26A to 27C.

FIG. 26A is a partial cross-sectional view illustrating a state in whichthe porous layer 320 is formed on the supporting substrate 310. Asillustrated in the figure, the inner surfaces 321 c of some pores 321are exposed at the surface 323 of the porous layer 320.

As illustrated in FIG. 26B, a thin film 390 having a low resin affinityis formed on the surface 323 and the inner surfaces 321 c. The thin film390 may be formed by, for example, applying a solution containing amaterial having a low resin affinity to the surface 323 and the innersurfaces 321 c and then performing drying.

As illustrated in FIG. 27A, the thin film 390 is irradiated with UVlight. Thereby, as illustrated in FIG. 27B, a portion of the thin film390 formed on the surface 323 of the porous layer 320, portions of thethin film 390 formed on shallow portions of the inner surfaces 321 c ofthe pores 321, and portions of the thin film 390 formed on regionscorresponding to bottoms of wide openings are exposed to the UV light toincrease the resin affinity, resulting in high-resin-affinity portions390 a. A sufficient amount of UV light does not reach portions of thethin film 390 formed on deep portions of the inner surfaces 321 c of thepores 321 and inclined portions of the thin film 390 substantiallyparallel to the irradiation direction of the UV light and being formednear openings. Thus, these portions are not exposed to the UV light. Theresin affinity of these portions is maintained at a low level, providinglow-resin-affinity portions 390 b.

In this modification, the thin film 390 is included in the porous layer320. The portions of the thin film 390 exposed to the UV light areincluded in the surface 323 of the porous layer 320. The portions of thethin film 390 not exposed to the UV light are included in the innersurfaces 321 c of the pores 321 in the porous layer 320.

As illustrated in FIG. 27C, the resin material is applied to the thinfilm 390 to form the plastic substrate 330. At this time, thelow-resin-affinity portions 390 b are present in the inner surfaces 321c of the pores 321. Thus, the resin material is less likely to enter thepores, thereby maintaining the porosity in the portion of the porouslayer 320 in the vicinity of the surface.

The high-resin-affinity portions 390 a is formed on the surface 323,resulting in high adhesion between the porous layer 320 and the plasticsubstrate 330. This prevents accidental detachment of the plasticsubstrate 330 from the porous layer 320 in the subsequent steps in theproduction process of the electronic device.

While UV light is used for the resin affinity treatment as describedabove, the affinity treatment is not limited thereto. The affinitytreatment may be performed by irradiation with light (visible light) orplasma treatment in place of irradiation with UV light, depending on thetype of the thin film 390.

Seventh Modification

The average diameter of the pores in a portion of the porous layer 320adjacent to the plastic substrate 330 may be larger than the averagediameter of the pores in a portion of the porous layer 320 adjacent tothe supporting substrate 310. In this case, a resin material used toform the plastic substrate 330 easily enters the pores. However, theportion of the porous layer 320 near the plastic substrate 330 has lowstiffness and thus has the advantage of being more likely to absorbstress caused by a high-pressure gas generated at the time of laserirradiation.

While the display panel devices and the methods for producing the sameaccording to embodiments of the present disclosure have been describedon the basis of the embodiments and the modifications (hereinafter,referred to as “embodiments and so forth”), the present disclosure isnot limited to the foregoing embodiments and so forth. The firstembodiment, the second embodiment, and the modifications thereof may beappropriately combined together. The present disclosure includesstructures obtained by subjecting the embodiments and so forth tochanges conceived by a person skilled in the art and structures achievedby any combinations of elements and functions in the embodiments withoutdeparting from the scope of the present disclosure.

In the embodiments and the modifications, the structures in which thelaminated substrates are used in the display devices have beendescribed. The structures are illustrative but not restrictive in allaspects. For example, even when the laminated substrates are used forelectronic devices except display devices, in particular, light-emittingdevices that emit light from at least part thereof (lighting systems,electronic advertisements, and so forth), it is possible to suppress thereflection of extraneous light. While the display devices includedisplay device elements in the foregoing embodiments, in the case oflight-emitting devices, display device elements may be replaced withlight-emitting elements.

A flexible display produced by the present disclosure is applicable toelaborate displays that can be fitted to curved surfaces, for example,television sets, mobile terminals, such as tablet computers andsmartphones, watch-type wearable terminals, and automotive interiors.

What is claimed is:
 1. A light-emitting device comprising: a transparentsubstrate having a first surface and a second surface opposite to thefirst surface; a light-emitting element and a thin film transistorprovided on the first surface of the transparent substrate, the lightemitting element being configured to emit light; a porous layer on thesecond surface of the transparent substrate, the porous layer includingan organic material and having pores; and a first layer between thetransparent substrate and the porous layer, wherein the light-emittingelement has a third surface and a fourth surface opposite to the thirdsurface, the third surface facing the first surface of the transparentsubstrate, the light is emitted from the fourth surface of the lightemitting element to outside of the light-emitting device, and the firstlayer is thinner than the transparent substrate.
 2. The light-emittingdevice according to claim 1, wherein the pores in the porous layerinclude a first pore and a second pore that is larger than the firstpore.
 3. The light-emitting device according to claim 2, wherein adiameter of the second pore is at least ten times larger than a diameterof the first pore.
 4. The light-emitting device according to claim 1,wherein the porous layer has a uniform thickness.
 5. The light-emittingdevice according to claim 1, wherein the porous layer has a thickness of1 μm or more and 1000 μm or less.
 6. The light-emitting device accordingto claim 1, wherein the thin film transistor includes a gate.
 7. Thelight-emitting device according to claim 1, wherein the thin filmtransistor is located between the light-emitting element and thetransparent substrate.
 8. The light-emitting device according to claim6, wherein the thin film transistor is located between thelight-emitting element and the transparent substrate.
 9. Thelight-emitting device according to claim 1, wherein the light-emittingelement and the thin film transistor are provided indirectly on thefirst surface of the transparent substrate.
 10. A light-emitting devicecomprising: a transparent substrate having a first surface and a secondsurface opposite to the first surface; a light-emitting element and athin film transistor provided on the first surface of the transparentsubstrate, the light emitting element being configured to emit light; aporous layer on the second surface of the transparent substrate, theporous layer including an organic material and having pores; and a firstlayer between the transparent substrate and the porous layer, whereinthe first layer is thinner than the transparent substrate.
 11. Thelight-emitting device according to claim 10, wherein the thin filmtransistor includes a gate.
 12. The light-emitting device according toclaim 10, wherein the thin film transistor is located between thelight-emitting element and the transparent substrate.
 13. Thelight-emitting device according to claim 11, wherein the thin filmtransistor is located between the light-emitting element and thetransparent substrate.
 14. The light-emitting device according to claim10, wherein the pores in the porous layer include a first pore and asecond pore that is larger than the first pore.
 15. The light-emittingdevice according to claim 10, wherein the porous layer has a uniformthickness.
 16. The light-emitting device according to claim 1, whereinthe light-emitting element and the thin film transistor are providedindirectly on the first surface of the transparent substrate.
 17. Alight-emitting device comprising: a transparent substrate having a firstsurface and a second surface opposite to the first surface; alight-emitting element and a thin film transistor provided on the firstsurface of the transparent substrate, the light emitting element beingconfigured to emit light; a porous layer on the second surface of thetransparent substrate, the porous layer including an organic materialand having pores; and a first layer between the transparent substrateand the porous layer, wherein the light-emitting element has a thirdsurface and a fourth surface opposite to the third surface, the thirdsurface facing the first surface of the transparent substrate, and thelight is emitted from the fourth surface of the light emitting elementto outside of the light-emitting device.
 18. The light-emitting deviceaccording to claim 17, wherein the thin film transistor includes a gate.19. The light-emitting device according to claim 17, wherein the thinfilm transistor is located between the light-emitting element and thetransparent substrate.
 20. The light-emitting device according to claim18, wherein the thin film transistor is located between thelight-emitting element and the transparent substrate.
 21. Thelight-emitting device according to claim 17, wherein the pores in theporous layer include a first pore and a second pore that is larger thanthe first pore.
 22. The light-emitting device according to claim 17,wherein the porous layer has a uniform thickness.
 23. The light-emittingdevice according to claim 10, wherein the light-emitting element and thethin film transistor are provided indirectly on the first surface of thetransparent substrate.